I've seen mods expand custom faction creation by allowing players to choose affinities and army compositions, starting heroes and even questlines, but what if we were to go a step further?

What if wanted to outright FUSE two factions together? 

Would we have to make a modded custom faction (for every combination) to do this? Or could it be done by allowing even greater  levels of freedom in custom faction creation?

I.E. 1 custom faction with 1 faction's leader, another's city/building assets, another's ship assets, 2 questlines, 2 sets of affinities and traits, ALL unique research options, etc.

LITERALLY a single custom faction that has (virtually) ALL things related to 2 (or 3) vanilla factions.