As much as I would love to see more of that setting, the main issue with Planescape 2, or Star Wars or whatever else, would be licensing rights. As far as I know, Atari has publishing rights to D&D videogames (feel free to correct me on this), and I can't imagine it being cheap to wrest that away without their fingers in the final product. Not to mention that WotC/Hasbro might have their own influence on it as well. Again, I'm not in the know, but at the very least, licensing issues would cut into the costs, and although I have no doubts that you would be able to raise a substantial amount of money, it would mean less for the game if you had to pay/negotiate the license. As for my own idea to throw into the ring, how about an investigation game with a Lovecraftean bent? Wait, don't go yet. Now I realize that Cthulhu and Lovecraft have gotten the same overexposed cult status that, say, steampunk has on the internet, but I think that a game that involves talking and investigating and less on shooting would be right up Obsidians alley and play to their main strength, namely conversation, dialogue, and choices. Don't focus so much on shooting elder gods, but focus more on interrogating others, gathering clues, and reaching conclusions. If you want to allow philosophical avenues, a la Planescape, it wouldn't be too difficult to throw in a bunch of nihilistic philosophy about man's infinitesimal influence in the dark void of nothingness that is the universe. Your detective can even have various personal crises that need to be contended with, such as alcoholism, a failing marriage, whatever, that could deter you from getting the "best" ending if they're not dealt with. Of course, when it comes to cosmic horrors, there's hardly ever a best ending.