Yet another variable, even if its an AI. I'm not talking about substantial investment, these would look at 200 credits and go, OMG, my AI brain says i could build 2 corvettes for that amount!. So AI fleets would be large simple minded fleets that had a few more command options then a regular "dumb" ai opponent.
Having them as an efficient source of credit investment to assist in attrition battles. In this way you would have a smaller fleet yourself, but your AI ally. This gives you the player more options, especially if these friendly sub-factions have more control options then just the simple "attack here, defend here" options (say you could order the corporations to build LRF!, build corvettes! you wouldn't que them yourself...). This would this would help the AI be less dumb to fleet composition.
The thing is, AI isn't terrible with attrition as long as its not costing you a ton of cash. This addition would just add another level to the game, imo.
Also, the sub factions need not necessarily be only AI. Imagine what could happen if sins actually had sub empires within the grander empires that say your kid brother or your girlfriend could play?
Co - Op sins in one empire could be possible, without having to have say 6v6 games added to multiplayer. These small factions would never be capable of having a lot of logistics slots to keep the game from minidumping. Something to possibly look forward to in sins 2, imo.
So if you don't have a co-op friend playing with you, you would have an AI variant. The sub-faction play could largely be limited to your sub faction friend, turning them for or against the main empire. In this way the sub faction player could assist the main faction player by over time creating another possible power bloc.
the game would then have an entirely new level of play.
Personally, I would prefer this because my girlfriend would rather play with me and assist in my RTS domination. This could also lure in new players into playing competative online matches by becoming someone's "second", and perhaps this second player could take over if the primary player minidumps!
actually the more i think about this idea the better it sounds.