I love the planes, the old Planescape was my favorite game setting. Including all its dense, esoteric systems and weird rules and what-the-hells. Casting spells in Limbo? Good luck!
But these things were a barrier for many, and even people familiar with D&D Forgotten Realms might have a hard time getting comfy in Planescape, including how the planes would alter spells. Larian doesn't strike me as the kind of studio that want to make anyone feel left out of the loop, or ask players to delve deep into exceptions to rules. Least of all in the tutorial part of the game.
I'd love to see another Planescape PC game, but that will never happen, since the setting is now just a backdrop for the prime world settings. But one can dream.
