Crap, now you've got my brain running.
OK, there are 3 areas that need to be worked on:
1) Game engine. The Infinity engine is KILLER. Got to agree with that. But it Bioware is playing that close to the vest, then that's right out. Maybe something using the Fallout or Diablo game engine?
2) Game mechanics. Here, I'd have to say 'Don't use T20.' It puts WOTC in charge, and almost forced the use of the Infinity engine. FFE owns Classic Trav, and could probibly swing T4/T5 game mechanics.
And wasn't Fallout originally supposed to use GURPS mechanics? "G:T, the computer RPG" using the Fallout engine?
3) Design. It's all about the STORY. Plot, sub-plots and tons of minor plots. This is where the real WORK would be.
Sierra hasn't put out a decent RPG in ages. Blizard, a sister company of Sierra, has the Diablo series, but that's only almost an RPG. WAY too linear. For something on the Baldur's Gate level, you'd almost NEED to use the Infinity engine, and now were right back to where we started, aren't we?
Hmm. Let me think some.