A game where you're an interstellar empire, going out and conquering primitive species to incorporate into your army, like many other alien foes in videogames. Species would be procedurally generated, and you'd create different kind of troops with them, using the semi-random technology you have. There would also be some other fledgeling spacefaring ones that would be the biggest threat, and the bigger you get, the more chance they have to band together against you.
For instance, you find a big, burly race in their iron age and conquer them. You've got a big plasma cannon that was invented for vehicles, but you create a kind of troop of the big guys that carries one as their weapon. With just the base of the species and the tech you possess, you can create as many kind of units as you want. There'd be options like whether they carry a piece of equipment, or whether it's attached cyberneticly, where the weapon is held/grafted, materials and structure of armor, that kind of thing. Your designs would be practically limited by the nature of each species, though, and certain kinds of equipment that might interfere with each other. The cost and time to produce and/or train each kind of unit would be calculated based on your technological capabilities, level of dissent amongst the species, and the different kinds of equipment the unit has.
Your troops would be stored only as the number of each kind you have, but randomly (or semi-randomly) you might be informed about "discovering an exceptional individual" of a species who has far different stats, and given the option to make a specialized hero unit out of them.
So, kinda-sorta-ish like a cross between Mount and Blade, Spore (space stage), and X-COM.
EDIT: additionally, you'd have to maintain cohesion amongst your army. You've got intensive conditioning and training (and possibly some kind of psychics mechanic), but your underling sentient species can still develop fear, doubt, and dissent. Depending on the nature of different species, taking their members and turning them into some kind of heavily altered cybernetic monster would appall and enrage them, and you might try something brutal by not allowing any civilians to exist and just making the entire species into cloned, brainwashed troops, but then the other spacefaring races might see you as absolute evil monsters, and not hold anything back (or agree to diplomacy).