Yeah, I could add a few of these new poptypes to the map in a few places. The horror worshippers would be a bit more difficult but not a big deal overall. It's nice to have more indy poptypes, having just 5 real different poptypes to choose from was making the galaxy look a bit under-diverse
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The one issue with horrors, is I'm pretty sure that they'll attack your own units... even other horrors. So probably if I'm going to place a horror in a province I should just place one. And it's possible the horror being in the garrison would cause an attack against the province. Btw you actually can summon horrors in combat. I don't know if you've taken them out of the mod though since no one uses blood magic yet.
Neoclidia doesn't have fighters. They have low hp high damage output warships and some drones. So I guess it could be considered, but those would probably be incredibly fragile fighters. Unless maybe they were used for the drones?