Hi,
I had the idea to split up the three races into subfactions like C&C Generals for example.
This would be a mod with no or few extra content just alot of coding work to change alot data and abilities. Some ships will be not available for one faction or the other but there will be also some variants like armed trade ships, TEC units mounting experimental weapons, Advent ships with ability-based PSI-weapons only, escort Cobalts with additional anti-fighter capability etc.
I'm still brainstorming on the factions:
TEC:
Usually the Trader Alliance was about peace and trade, with the Vesari peace became war and there is also a faction for the rest

More pirate techs
Trade Department: More like the original Trader Alliance. Really efficient and early trade. Trade ships and stations have defensive weapons/abilities. Strong economy...naturally
War Department: A steamroller faction that needs to buildup mass before it strikes. The research tree could be divived into 2-3 strategies. You have to research a really expensive gateway tech to unlock one strategy (basically deciding for one until late game).
Civil Department: Home for stuff the other two don't have/like. Culture, colony techs, lots of defensive equipment.
Vesari:
Survey Fleet: This force is the eyes and ears of the exodus fleet. The faction would be fast, mobile, and raid/intelligence oriented (bounty efficiency). Few colony techs, more local effects and research, less global stuff. More phasejump techs.
Exodus Fleet: The bulk of the fleet. Mostly like the standard Vesari. Mobile resource gathering (Refineries).
The Exclave: Born of the 10 years in TEC space some Vesari dramatically changed their millenia old ways of living (e.g. Trade). They are focused on development, colonies and building. More large research/structure projects.
Advent:
Not much to work with. Maybe caste based factions. One should be definately more PSI ability based. Another one may be a leader caste, having the most powerful equipment and lots of controlling stuff (culture).
What do you think?