Actually, I think Pappaclart's post is a perfect example of why motorcycles should not be in any Gran Turismo. And I keep forgetting that I discussed the subject with my autocrossing relative years ago when the GTHD images were floating around with the motorcycle in the selection list. He wondered how that could even work, because the power to weight ratio of even an average bike is ridiculously high compared to a car. Rain would equalize things a little bit, but otherwise, bikes would leave any car but an F1 in the dust on curves, so the only way they could even compete together is on something like the NASCAR road course tracks, with mostly straights and sweeping curves.
People complain about rabbit cars now. This would be worse. And many GT fans, like me, just don't care for bikes. I never picked up Tourist Trophy, even when it was in a rack for $5. And face facts, it hasn't fared well in sales compared to most other car racing games, selling less than three-quarters of a million units globally. Since some here like to quote GT3 figures so much, this is less than 5% of GT3's sales.
For that reason, having a Tourist Trophy II section of GT6 makes some sense, completely segregated from the car racing, but can you imagine the outcry from fans pointing out that cars would have to be sacrificed in order for the team to model a number of bikes? I want those cars, not a bunch of motorcycles, no matter how cool they might be.
I think this notion would cause more trouble and hurt feelings than its worth. Bad, bad idea.