GLEEGLEEGLEEGLEE I like the sound of that idea. Can anyone say interstellar crime syndicates?
So, in my 4x project (Now aborted because of work), I decided that rather than just make agglomerated species empires, to allow a more granular kind of thing, even allowing (If the player made a series of very tricky political decisions and rode through the civil war) another species to usurp the facilities and bureaucracy of the player species if the player got sick of the race he was playing as.
Course, that game also had all development of empires handled by the AI, and the player expended influence that he accrued at risk of being discovered to influence matters, say, sending a fleet to protect an unimportant colony of rabble rousers.
Naturally, my project only got to me making a map that was little better than a spreadsheet when I noticed the hilarious tendency of 90% of the species self destructing and the remaining ten percent that actually got off world meeting and promptly destroying each other. So, yeah.
Uhm, point was, will you be incorporating inter species migration and cultural conflict kind of like say Victoria from Paradox games, or not? Cause it sounds like your penal colony system could handle it. Y'know. If you wanted to do that.