So, let's assume it's a RPG. If it's "dormant", it's also (probably) not a franchise someone else is already working at, or something anyone has been doing for quite some time. With both NWN 2, KotOR 2 and now Fallout: New Vegas, Obsidian must have gained quite the reputation for continuing the work of others. Also, the mere usage of the word "franchise" implies that it is just that, a franchise of some repute (and not just a sequel to a single game). Also, Obsidian would probably not strike a deal with a publisher with a weak economy. Or maybe they already hold the rights?
Would it also be reasonable to assume that Obsidian wants to create a game in which they can recycle their art assets from "Alien: Crucible"?
So, let's look at the big publishers and the franchises they hold.
Let's just say this: whatever it is, it's bound to be a big thing