Planescape Torment does have a legion of fans. It is at least considered for some a respectfull title.
Every since obsidian was found, it is mentioned as the "former creators of Planescape Torment, Fallout and stuff" so it does give them credit.
And most of all they didnt have to reference anything related to planescape in NW2. No one was expecting it. It wasn't needed fot the game to be good, and they added it anyway. I don't know, maybe to see how people would react? Or maybe I'm just hoping too much.
Anything that might come in this universe would be awesome, mmorpg (that doesn't suck) or a kick ass single player game with or without the nameless one. Maybe with fall from grace as main char as someone already suggested.
ps: sorry for my english.