Just to clarify, this won't use Planescape. As Colin McComb explained, WotC retired Planescape for 4th edition and he approached them but they have no interesting in licensing it out. This wouldn't use the Planescape setting. Nor would it pretend to follow up directly on PS:T's story, both McComb and Chris Avellone have said that's not much of an option.
Instead, it'll take the core goals and themes of Torment and write a new story in a new setting that shares similar goals and ideas. Use Torment as a label for a thematically tied franchise. Dense writing. Philosophical themes. A personal story. Subverting RPG tropes. But not Sigil, not The Nameless One.
And with this my reservations have evaporated.
I just get this itch whenever somebody says PS:T sequel ....