Since the original article is in French, Obsidian Entertainment's Chris Avellone has published the English version of an interview he recently did for foreign website Polygamer. Alas, what could have been:
8] Tell us about one or several of your projects which you would have loved to release but you could not for various reasons. There appears that each creator has at least a cursed project of this type in his bundle, so do it, please frustrate us with this game we will never be able to play. Moreover, with the time, what do you think about this project(s) which stay on the paperboard and why do they stay like it ? Chris needs to win the lottery so he can bring his ideas to fruition without having to worry about profitability and appeasing suits.
I wanted to do a Planescape Torment sequel called Lost Souls where it took the lives of Deionarra, Ravel, Dak'kon and others from the original and told their tangential stories in an RPG format before and during the events of Torment.
I also wanted to do one other game set in the Planescape universe that wasn't tied to Torment itself, called Planescape: Tesseract. I actually turned a sample of the premise into a 2-3 hour pen-and-paper game session that played at GDC one year with a lot of press folks (and Ray and Greg from BioWare), giving each of the folks a pre-made player character and a time limit to accomplish their goals. I really liked the character designs, and I'd love to develop those characters, but most of them only work in the context of a Planescape-style universe.