You could use command blocks to help with most anything (Since it's GC4). When more addons are updated to GC4, you could use a lot of them (See the Giant Galaxy Modpack) and host interplanetary warfare! The Overworld will be a kind of hub/neutral planet. Players should have an accelerated start. From the Overworld they can get a Team/Faction's Homeworld.
Each faction would have their own kinds of motherships (maybe not the best, since 2 can't be in the same dimension) that they build to their faction's theme. They can attack other faction's Homeworlds to try to eliminate them. Factions can take over non-Homeworld planets to get some kind of bonus. (Better resources, lighter blocks for motherships, more powerful weapons?). Each planet has 1 base, and is ruled by 1 faction at a time.
(I realize this would be a massive project, but I think it's kinda possible, and cool)