Hmm. I think I'll have to be the downer for this game idea. First, an article from The Escapist.
http://www.escapistmagazine.com/articles/view/issues/issue_221/6582-Why-Your-Game-Idea-Sucks
Now, admittedly, it'd probably not be a stretch to see Yahtzee be able to convince some people to help him make this game, but still.
Also, I genuinely liked it. It was a nice game idea. But, I think it had a little too much going on. It doesn't have enough focus to please any certain crowd. The rabid party-going Guitar Hero fenatics would find it too much like a real video game to enjoy it, and the mainstream gaming crowd, I think, would be quite pestered by the inability to move during combat but the ability to move while driving the van. Also, the combat would be like playing some strage off-shoot of Tetris in 5 different planes. Enemies slowly lumber toward you while you try to clear them. You may be killing them instead of making lines with them, but it's still quite similar.
But, okay. Yes, it's a good idea, and I would probably get the game if it was on a big budget.