Re: Hero System Good Idea/Bad Idea...
This of course assumes GURPS doesn't make your head explode.
Actually, they only got through the Mage core before White Wolf pulled the plug on the GURPS conversions. (Why is something between the two companies; probably only those directly involved truly know).
One of the settings that GURPS never got to was Wraith: the Oblivion, one of the great disasters of RPG history. You played a restless ghost who spends most of his time feeling awful, with limited interaction with the real world. It's sort of like an RPG about being in Hell or Limbo. It proved very unpopular and went almost completely unplayed.