First of all, I feel the need to say in advance that I do enjoy this mod and seems well done for what it is. That said, I have feedback.
On the easily obtainable ships(Hedone, Tumbleweed, butterfly, civilian capitals, and probably a few others I forgot that I found in the market often): There's not a whole lot I have to say about these. They exist and they seem to fit, but I personally didn't see much use for them. They were not out of place in AI fleets and the combat ships performed well enough for what they were.
On the seemingly only salvageable ships(557, Onyx, Siegfried, Marksman, Trailblazer): The ones I could find among these were quite interesting. The 557 was fun to use for a minute, but fell off insanely hard against most things with a bigger gun. It has a lot of speed, but not so much that you can skip out on a speed hullmod and still circle around any cruiser. Served a purpose and was fun to use, but not game-breaking. The Onyx was odd to say the least. Front focused weapons and Temporal Shell work quite well together, but it's also rather slow. Very normal of a capital of course, as otherwise it would not need support. It very badly needs support against even 2 targets if it can't take one down or flux it out in time. I didn't use it that often, but when I did, it didn't do that bad. The Siegfried was exactly as the description made it out to be. Defender, not an attacker. Agonizingly slow, but good enough protection overall to fend off most if not all small crafts within range. As for the Marksman/Trailblazer, I never got to use them, just found them in combat a single time in the playthrough, but was unable to recover them. They seemed to do fine(at least in the hands of the AI). Can't say much on ships you haven't used though.
On all the spoiler ships...
Spoiler
First one I found was the rampage. Quite menacing when I first found it, as it was soon after I started and I barely had more than one destroyer and was only set up for exploration and low end combat. When I had enough to go against it, it was an interesting enough fight. Nothing too fancy, but didn't go down easy. My only question would be why did it start to try to flee? I thought it was an AI, and they never seem too keen on running away.
Second one was the Cataclysm. This one did give me a good bit of trouble because of the entourage it had with it. After I did enough strike runs to get rid of all them and isolate it, a few capitals and a destroyer or two took it down easy-ish. Losses are to be expected. Either way, a more interesting encounter than normal. I did recover a few zealot ships, but did not use them, as I had better things at that point.
Third was White Dwarf. I literally never have a good time fighting the remnant and this was no different. Painful as always, and took a lot of my ships down with it. I didn't even get much of anything after the fighting was over, which was mildly disappointing. Was hoping for more than the normal number of Alpha Cores recoverable or just something other than a slow clap. Not even special text.
Fourth is Nova. As with White Dwarf, this was also painful. It actually wasn't as painful as the other though. I didn't try the same thing, so I imagine that was the difference though. So after I killed it, nothing happened. Nothing at all. This time it was more than mildly disappointing.
Fifth and final(I think) is Safeguard. I don't even know what the main cannon does. Phase ships tore this thing to shreds with very little resistance. The meager payout was expected of domain tech. Was by far the easiest fight among these. Nothing more for me to say on it.
So what is the point in killing all of these? Are there more of them that I don't know about? I've explored literally every system and that is all I've found. Are there quests that I didn't find that give you more applause than your own 2 hands when you kill them? I want to feel like I accomplished something when I finally overcome each of them. I know exactly when they are not recoverable, and I probably wouldn't bother using them anyway, but I got the weapons they were using and nothing else. I found the derelict Onyx in the same system as Nova(I think it was that one, either that or it was White Dwarf), but I don't know if that's just a coincidence. So maybe the Onyx was the "reward" for one of them? I wanted a blueprint of something, or just a little something. It felt basically pointless to kill all of them. I got their weapons, which are nice, but it didn't feel like much of a reward. Maybe I'm being picky or spoiled by other mods. The only other one I will bring up here is HMI. After you do the hidden stuff in that mod, you get blueprints of stuff. It's not terribly easy to get, and it's not broken, but it's something. I didn't even see a text prompt come up when I killed them. Just the normal stuff. I did use some of the plagued weapons, and they are good, but not great. Seeing as they reduce CR, I prefer to use other weapons. The exotic weapons are quite good though. Not by a long shot, just rather good.
Anyways, this mod is rather nice and it is one of the mods that actually made me explore the entire sector looking for stuff.