You're not going to believe this, but I was thinking of the same thing this morning on my way into work. WIth the work I've been doing to support text-to-speech, I've been thinking of other things that would make me look at my empeg display less, and a "heads up display" would be cool. The idea of playing the current artist/title via text-to-speech doesn't really sound too appealing, having it proejcted in a little area of the windshield would be much more ideal.
I know Kenwood has a heads-up display thing but I've never seen it in action. And it's limited in what it can display. It'd be a neat project for someone, though.