The empeg uses PWM to achieve it's 2bpp.... ie, it turns the pixels on and off fast enough that you can't see it, and refreshes at 40 frames per second. (IIRC)

The problem is that the data rate just isn't there over serial. I'd be inclined to wait a year or more before doing such a project - Noritake are doing some great stuff with multicolor VFDs, and ethernet is starting to progress into microcontroller cores. Once that happens, perhaps an ethernet -> multicolor display becomes a possibility. (Of course the multicolor would only really be useful as a means of getting car interior matching to a fine art - I can't see the empeg guys releasing player/visuals software that'd natively support multi-colors. But even that'd be great.)