Well, what do you want them to make? Obviously speculation at this point, but I wouldn't mind seeing a spritual successor to Planescape:Torment, with all the weirdness and wonderful ideas that it might bring. Of course, some may say that we already got a variant of that in Mask of the Betrayer. Me? What I would really like is if Obsidian did a much better version of Arcanum. There's still a ton of ideas to explore in the steampunk vs magic genre, and gelling it with Planescape's sense of mythic philosophy might bring about something unique, especially if Avellone is helming it.