Not a sequel. Naturally, there are many single player RPGs we'd love to see continued but, even without the concern of licensing fees, there's more value in showing that not only are deep, single-player rpgs worth publishing but you don't have to rely on an established brand (even a lesser known brand like Fallout was to the xbox generation).
A couple of things we've been told also come to mind. One, that Obsidian's Onyx Engine has been designed for role-playing games specifically, and two, that Dungeon Siege III didn't include an editor as the earlier Sieges did, because that would have been as consuming as the game itself. The important thing was assuring the quality of the core product. So with that, I would suggest that Obsidian uses Onyx for whatever you're already planning for it, but allow us to use Kickstarter to motivate you to put together a package of tools, tutorials, and advice for us. A big part of the Double-Fine success seems to be the language they used. Essentially, "Here's you're all-access pass, welcome to the team." This would be similar. We would help you give us the means to develop alongside you, in the spirit of less-than-modernly-marketable RPGs.
I can picture that Kickstarter spawning numerous other Kickstarters to realize all of those Fallout/Planescape/Arcanum fantasies that modders are already trying to force into editors that are far from ideal for those properties, or putting together in games that are already showing their age.