Alright, in typical Bio fashion, I saw this section and my brain exploded with ideas - some new, others old and modified to fit - and I dunno which one is best. So, at the invitation of Naz, I'm making a thread here to ask for advice. (Mods: Some of these ideas might not really work out here. Let me know if that is the case. This especially goes for the third one, Dei ex Liberis.)
The first idea I thought of is based on my ill-fated Succession of Shifters RP, which has been attempted a total of seven times on various sites and always dies way too quickly. Maybe, with more resources and players, it could work... Shifters is about the children of a king, who dies unexpectedly, without naming a clear successor, leading to a succession battle. This is made more interesting by the fact that the whole family consists of nigh-immortal dimension-shifting demigod-like people with mind control powers and stuff - in other words, they can bend entire realities to their will and make them fight for them.
Second idea was also based on an old RP - the first one I tried on RPA, I think. This idea is probably not going to get much interest but I'll mention it anyway... Wonk_Sauce. Comedic/apocalyptic sci-fi RP set in the far future, where the intergalactic Generic Union was shattered by disastrous contact with an extradimensional race known as the Defilers. In the original Wonk_Sauce idea, there were only three main factions: the Mailmen and the Psionics Wing (remnants of the former Generic Union) and the Defilers. If this idea is used for a WBRP, it would have many smaller factions, with the Mailmen and the Psionics Wing possibly being the largest two.
My third idea is called Dei ex Liberis ("Gods from Children" in Latin), and tells the story of several children who become godlike in power. Now, this may seem odd in a faction-based RP, so let me explain: They are granted their powers by an (automated) alien ship which abducts them, trapping them on-board. The ship does, however, have "viewports" which allow the kids to view Earth and use their powers on it... So in effect the kids are leaders of factions consisting of the people they can recruit. (This idea may not work here, and I understand if that is so.)
...Also in typical Bio fashion, I forgot all my other ideas. I will post them later if I remember them.