Major feature-request here, but I keep coming back to this.
One of the main things this game's missing that Mount and Blade has, that Escape Velocity has, that is even in Star Control II... is the ability to have a battle with multiple parties, some allied, some enemies. The more I think about it, the more I think that this is a vital feature.
Why:
1. Being able to fight alongside an ally is fun, even when it's frustrating. Allies may not be bright, they aren't going to follow your orders, they may make your life difficult, but it involves us in the RPG aspect of things so, so much more.
For example, in an encounter, we meet some Pirates. The battle generator automatically creates some friendly ships of (insert allied Faction here) that are assigned to Side 2. They're merchants in weak vessels with a couple of escorts. If we save them, then we get a reward dialog at the end of the combat. If we help the Pirates destroy them, we take a relationship hit with the Faction. Or we can just use them as disposable meat shields, in which case we don't get any reward, but maybe we get through a tough fight without serious losses. No matter which choice we make, it's interesting and it's an emotional choice, and if it was backed up with some post-combat Dialog events, it would really enhance immersion.
2. Having multiple parties in a battle with different goals would make battles much more entertaining at the grand-fleet level of play.
Right now, grand-fleet play is the weakest spot in the game, imo.
By the time we can do it at all, we've buffed our characters to the point that they're well-nigh godlike, our ships are powerhouses... and play is straightforward- go cap the necessary points to free up FP, deploy forces required to handle the opposing force, plow forward to victory. If we're experienced players and understand the battle system, we pretty much know whether we'll be able to win or not really early.
If, however, a third party enters, it gets a lot more interesting. For example, if the third party is enemy to both other parties, then we have a three-way contest for possession of battle resources and flanks are going to be uncovered early. We can direct our fleets to take on one side, hoping the other enemy joins in and helps us get rid of that threat, or the AI teams may gang up on us, or decide to fight each other first, then fight us if they still think they can win. No matter how it goes, a three-way fight is usually more interesting and more likely to lead to memorable moments.
3. It would allow for construction of all sorts of interesting scenario play. The situation with the pirates in point 1 is just one example; from that basic template alone, many interesting situations could be built. But let's imagine some other possibilities:
A. You stumble upon a Pirate Station upon exiting a Wormhole. You have enough fleet to attack it. However, when you arrive, you discover that the Pirates have hired a Merc force; a dialogue ensues, and if you say the right things or enough money changes hands, you can either fight the Mercs, have them as allies, or they'll fight for a while but withdraw if the battle's not going well for them or their employer.
B. You encounter a Hegemony patrol. You're on bad terms with them, and things look dire. But a timer / RNG in the battle code decides that, 5 minutes in, a Tri-Tachyon force arrives, giving you help. Or do they hate you, too? Either way, things just got dramatic.
C. You line up your many, many allies and decide it's finally time to take on the <insert boss> homeworld. You and your allies fight through many challenges, but up ahead, the Ultimate Boss Fleet awaits. You order two allied fleets to attack, and an auto-battle starts, and you join in. Three fleets, buffed by your skills, converge on the Ultimate Boss. Having all those allies really paid off, and unlike how it would work right now (if we could order allied fleets around, but that's getting ahead of the development timeline) you wouldn't just send them to die, piecemeal, but would make a grand armada and fight the Good Fight.
D. You have a Frigate fight in early game, in an Asteroid belt. Turns out that there is a Mining Base hidden here, surrounded by mines. Do you use this as an obstacle, putting yourself on the other side of it? Do you attack the Base to get more loot at the end? Do you ask them for help?
E. During an encounter, a neutral party shows up, picks the losing team as an ally and tries to be a Good Samaritan. Whether the player was winning or losing, things got interesting and the post-battle results could be important. Perhaps the player even retreats, lest his fleet destroy the neutrals and cause a war.
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Anyhow, that's it in a nutshell. I think that there's so much depth that could be had with this feature and I've barely scratched the surface.
From an AI perspective, it shouldn't be too hard (at least, I can't see the major problems over here). Some sort of Faction relationship check for each side at the beginning to get hostile / friendly status, fleets could enter from all four sides of a battlefield, otherwise all is how it is now, short of scripted scenario stuff. The hard part would be giving the Fleet controller AI a bit more nuance in situations where > 1 side is the enemy, but it doesn't have to be wonderful or super-smart to be Fun.
Lastly, none of this works or is even practical if Auto-Battle is over instantly. It really should last a lot longer than it does as it is, simply for immersion's sake, but in this case, it would be totally necessary. Again, I don't see huge obstacles; simply let the player join in or not, and if they do, then it goes to the battle an assigns the player a side of the map randomly.
Anyhow, I know that this is probably too far for 0.6, but I think it's genuinely something the game needs. If working with Exerelin and the earlier Fleet Control mods showed me anything, it was that interactions where you cannot personally join fights are extremely limited and less fun than they could be. I think this is a must-have item at some point.