We've discussed the problems associated with making more playable factions before, and they all still apply here as much as anywhere else. If we were to make a GC centered around a bunch of different Imperial factions, you'd still only ever be able to play as one of them unless we made multiple copies of the same GC, but it's getting cluttered as it is, and the more minor Imperial factions we break everything into on the Galactic map, the sooner we get the freeze. Basically this means I try to limit it to 2 Imperial factions per GC; the playable version, and the rest get grouped together.
This is why in Fractured Empire, you get the Empire run by Isard as the playable option, and then Zsinj and Pentastar are grouped. Otherwise you get a faster freeze, and you get Warlord factions that are complete pushovers by the time you get to them, since otherwise they spend the whole game destroying each other. In Hunt for Zsinj (2.0 version), you get Zsinj as the playable faction, Rogriss working with the NR/Hapans, and Teradoc in Maldrood, and 3 groups is about as much as I think we'll ever break up the Warlords.
Weird explanation of Imperial Divisions follows. I researched this as I wrote, so don't worry if it's a bit off, that's not the important part.
If we were to do the pre-Isard GC we were talking about before, for another example of how I'd divide the Imperial facions, the exact distribution would depend on who exactly everyone would want playable, but there seems to be a few distinct major groups at this point; Zero Command under Harrsk, Greater Maldrood under Teradoc, Eriadu Authority under Delvardus, Zsinj's Empire in the Quelii Oversector, Kaine in the Oversector Outer/New Territories (Pentastar Alignment pre-7ABY) and Sate Pestage/Isard and the Ruling Council territories/Ciutric Hegemony. There's also the New Republic. Basically it's unfeasible to distribute the groups all on their own, that's way too many active factions over too much territory; the game would freeze after 40 weeks.
I'll just simplify things by saying the Oversector Outer (Pentastar) is the playable group, the point here is the logic behind the divisions of the Warlords, so it could be shuffled around a lot depending on who's playable.
Playable Remnant = Pentastar Alignment
Group 2: Zsinj, Delvardus
Group 3: Harrsk, Teradoc, Ruling Council
New Republic
The key points here are 1) don't expect a GC with like 5-7 different Imperial groups, there are too many problems inherent in that kind of a situation unless Petro/LA decide to release an engine patch to fix the freeze, and 2) don't expect GCs single GCs where you get the choice of playing a bunch of different Imperial groups unless we get workarounds that aren't extremely clunky. The far more likely/reasonable option is more like Hunt for Zsinj, where the focus is on one or two groups. Smallpox would understand those options infinitely better than myself, though.