I came across this website a couple of days ago looking for a renderman compliant/reyes renderer that ran on GPU.
Basically, I think this guy is the first to publicly state he's made one, but other people must being making their own. I think a decent attempt at a GPU-based renderman renderer would fill a gaping gap in the renderer market and possibly get a large share of it (if at the right price).
I reckon it would get snapped up by lots of media/entertainment studios, especially if it was integrated well in the host app, like dna's 3delight for Softimage/Maya.
win 7 64 | q6600 | 4gb ram | gtx 260  | driver nvidia 197.13 | SketchUp7 | Softimage 2010
win 7 64 | i5-2500k | 16gb | gtx 570 | driver 275.33 | SketchUp8 Pro