i have to disagree with you Rushyo, I've done a TC before and they are not near as much work as an actual game Even when compared to a mod for a game like Starsector ( relatively low-bar of entry for assets ), an actual game requires: original sound work, original music, and a qualified coder in ways that a mod does not and never will.
I've written mods with their own scores and I've developed full games without original sounds/music. Whether it's a TC or not is irrelevant. That's entirely dependent on the license you're working with. There is no direct link between being a TC and the need to create your own assets. There's certainly nothing that says working on a Total Conversion means you're not a 'qualified' coder or using those skills. Java is Java is Java. OpenGL is OpenGL is OpenGL.
This Battlestar Galactica TC is more complex and time-consuming than my current Unreal Engine 4 game that's taking advantage of all the latest engine features, has concept art, complex 3D animations, its own sound track, plenty of tricky shader code, etc. The fact one happens to be a mod is really neither here nor there. The distinction is in the relative complexity compared to the base they're being built on. My UE4 project is a Rainbow Six: Rogue Spear-style FPS with cutting-edge graphics and UE4 makes that relatively easy since it's purpose built for that sort of thing. Most of the mechanics already exist, and thus the desired dynamics don't require too much work to achieve. My BSG mod's dynamics are largely based on a bunch of social mechanics, which little to no engines offer a base for. So the latter was always going to require more work.
A game's complexity to produce is defined on its complexity relative to the already provided functionality of the engine its using. Writing 8-bit Elite in assembly is a massive job, writing an awesome looking 3D shooter in CryEngine is (relatively speaking) not. To my mind a mod isn't a total conversion unless it was designed as a separate game. Many things labelled as 'TCs' are just extremely elaborate mods for video games that offer exactly the same play experience, the same dynamics and aesthetics, as the game they're built off. That's cool, and maybe even entirely suitable for the IP being used, but isn't a "total" conversion because the game's design hasn't changed, only the assets and code. It's fundamentally offering the same experience to the player, just with a re-hashed skin.
For example, SS+ greatly (IMO) improves upon the aesthetic goals of the original game. It doesn't add any, though. I play SS+ for exactly the same reasons I'd play Starsector. That's the intent of the mod. It plays around with the existing mechanics, doesn't do anything too frightening with the dynamics, and ultimately serves the same aesthetic goals. The same goes for faction mods. No matter how big they are, and even if they alter the dynamics (by, say, introducing a new missile that creates a new style of play), they are still fundamentally designed to be played for the same reasons you'd play Starsector. They're just trying to improve the existing experience through variety and polish.
Creating a total conversion of an IP is a little different. The IP, in most cases, has it own aesthetic that doesn't conform to the game's existing aesthetic. The 'survival' aesthetic that is central to Battlestar Galactica barely exists in Starsector. Occasionally you might get stuck in hyperspace without much supplies and fuel, but those mechanics are not used by Starsector to create a constant focus on the 'survival' experience. The BSG TC takes those mechanics, builds upon them with new mechanics, and creates a new dynamic or two that are explicitly designed to serve the 'survival' aesthetic, creating a different experience for the player.
There are also certain elements of Starsector where it has an existing aesthetic that fits with the Battlestar IP, but are completely mechanically inconsistent with the BSG IP. An obvious example is the faction relationship system. It offers mechanics that create a dynamic of 'relationship management' based on trying to keep the various factions happy, or not, in order to achieve gameplay goals. This fits with the Battlestar universe, where Roslin, Adama, Baltar, etc are constantly fighting over political credit and their relationships are critical to the narrative and the tension.
But what SS thinks of as 'factions' are designed under the assumption that they have a relationship with the player. In the BSG universe, there's no central 'player'. What's important is the faction's relative power and morale to each other. So the BSG mod has totally different mechanics and dynamics based around 'power' and 'morale', that ultimately serve the same aesthetic goal that Starsector does through faction relationship management (and, indeed, trading, which has roughly the same aesthetic outcome even though it's mechanically very distinct). This new set of dynamics for BSG also has to be deep and interesting enough to completely surpass not only the existing faction management system, but compensate for the missing trade functionality. That trade functionality which has very little place in a BSG IP, as it would detract from the 'survival' aesthetic, whereas in Starsector there's barely any survival aesthetic to hurt, so there's no harm is having it.
This sort of problem gets at the heart of games design, and indeed there are taxonomies and game design mantras that I've used to draw these conclusions. These aren't questions a typical mod deals with. A total conversion, however, ought to be defined by exactly these sort of changes. If these sort of changes don't exist, then it's not a 'total conversion' because fundamentally it's not altering the design of the game to provide a different experience, it's just enhancing the one that is already there. I can't stress enough that one isn't better than the other, but to me a TC is absolutely defined by this distinction. Unfortunately it's not one people who haven't written games across a number of genres and engines are generally familiar with.
Incidentally, this is why I'd also love to see a Trek mod in Starsector, as you mentioned. You could build a really great experience without detracting from any of the core aesthetics of Starsector, unlike a Star Citizen mod. You wouldn't need a TC to build something that totally captured the Trek feel and resulted in enjoyable gameplay. You could do it without being a TC. Sure, it'd feel more Voyager than TOS, because you'd be laser-focused on the combat and the factions, but it'd still be Trek.
But then we have to ask why I'd pick Starsector as base. We could dismiss Starsector as completely unsuitable for a BSG mod, but that would be incorrect. It still retains many mechanics, dynamics, and aesthetics in common with BSG. Not as many as, say, a Trek mod, but then
nothing else does. There is no engine more suitable for what I'm trying to do with BSG that I'm aware of. I could make it in Homeworld 2, but then I'd have to throw the political stuff (which comprises the large majority of what makes the BSG IP) out of the window. Same with Freespace. These mods already exist. But all of the existing BSG mods I've seen are entirely focused on ship combat, and use ship combat engines as a base. They forego many of the reasons you'd watch BSG as a series.
If you watch BSG it is almost entirely politics and sociology. Space combat is a sideshow to move the plot along. Most of the 'big battles' in BSG, of which there are very few, are just a backdrop to some political dealings. The biggest battles
largely or entirely happen off screen, because they would detract from the point of the series. Thus, to really capture as much of BSG as possible, and thus appeal to the same things that make the series interesting to viewers, a game
must try to provide those political aspects. Diaspora made a decision to focus on providing heavily on a sim aesthetic with a BSG skin, and it did a bloody fantastic job, but that doesn't mean it's the only way you can make a BSG game. The 'flight sim' aspect of the BSG IP is only a minority aesthetic, and there's a severe over-representation of sim games over other aspects of the BSG universe.
There is no base engine I'm aware of that has these mechanics, but Starsector definitely comes the closest. It has classes for characters and their AI, it has basic faction handling. It can handle ballistic combat just fine, although the niceties of making that dynamic and fun on its own do need to be addressed. But it's still far better than starting with nothing, or trying to use any mainstream engine. Even if the mod ends up being 75% my own stuff and only 25% Starsector, that's still 25% saved. In that sense, Starsector is a real time saver. I just didn't go in to it with any illusions that Starsector itself was going to solve most of the game's design for me. I fully intend to build a world that realises whole new aesthetics, dynamics and mechanics across the board, only utilising Starsector where it either a) does a fantastic job of serving the BSG IP (like the Newtonian physics and supply/fuel mechanics, fleet management) or b) is 'adequate' enough at a particularly difficult job that I can offset that work until the later stages of development (most of the combat dynamics fall in to this category).
This is why I love games design. This is not a simple problem. It can't be solved by simply hand-waving. To do it well requires knowledge of games production, experience of many delivered projects, DEEP research in to the IP, lots of sleepless nights, and an obscene amount of hardcore dedicated play-testing. This is a tough games design problem, of exactly the variety that makes it my favourite professional skill. You couldn't muddle through a project like this as an artist or a programmer. To do it well requires a games designer.
I think any Star Citizen mod is likely to run in to these same questions and constraints. You could create a Starsector-feeling Star Citizen mod, but without work and design you'd be taking out many of the core aesthetics of SC (the simulation aspect, obviously, but also the 'wing commander' feel and the social aspect of multi-crew). That doesn't leave you with much value from using the Star Citizen IP in the first place; you might as well just play Starsector, or you have to understand you need to make big changes. This comes back to what Tartiflette said: You can't get rid of core gameplay mechanics from Starsector that will damage the aesthetic outcomes IF you don't have a serious plan for adding new ones in. But then, I'm arguing that's EXACTLY what defines a total conversion.
In that sense, I think a good Star Citizen total conversion could work just fine. By definition, though, it would require inordinately more effort than a typical Starsector mod. The assertion that modding for Starsector is easy, ergo making a Star Citizen mod is easy, is the thing I don't think is logically sound. I think making a good Star Citizen mod would require relatively more work and skill than, say, a good Star Trek mod, because it requires going further away from Starsector. And even that would again require even more relative work and skill than a custom IP purpose-built to build upon the aesthetic of Starsector. Ergo, I wouldn't recommend it as a first project, I'd use another IP.
I had hoped to spare the long-hand explanation of my rationale for such a relatively simple point, but meh. Sometimes complex ideas merit a complex explanation.