I posted this over at Harmonycentral. Not a lot of response over there. One guy said he didn't know of anything. He suggested I would have to create my own out of gigapiano, Garritan strings, Dan Dean stuff, etc.
I don't know how many people would be interested in such a thing, but I think it would be really cool if those people could get together and create an awesome GM bank of say 5 CDs. One piano and electric pianos, 1 bass and guitars, one horns/brass winds, one strings, and one synthes/pads/whatever else. Surely one could fit a GM drumkit onto one of those CDs.
I'm just brainstorming here, but it seems that any Gigastudeo user would buy this so as to have a decent sample of all these sounds, and could still buy all the huge individual items if they are that serious and/or proficient.