I would love LOVE LOVE a Planescape Torment sequel and would easily pledge $200 for one.  That said, I understand that the D&D rights would be expensive to get, but maybe the game could use the Pathfinder license instead.  Pathfinder is basically D&D 3.75 and it has a lot of "planes" lore that is fairly similar to Planescape.  So a Pathfinder "Planescape" game would be extremely similar to a D&D one.  I think that Paizo may allow Obsidian to use their license for much cheaper as well.