If this happened, mind = blown. Planescape is my absolute favorite traditional rpg. I thought this wasn't possible due to the setting not being supported as an official D&D thing anymore? If there is one developer that can be trusted with this, it could only be Obsidian.
But it's not really a traditional RPG...
Yeah, that's what I'm guessing too. A new game in the same setting, but not a real sequel to Torment. I can't imagine it would continue the story of The Nameless One or something like that, because that story is finished.
Seriously, a sequel would be really out of place. Like, "Planescape Torment 2: Torment of the Planescape". I would pull a murder-suicide (this is hyperbole, guys).
A game set in the same universe with Chris Avellone working on it could be nice, though.