Ok, if they did find a way to make it entirely different than Forza's Auction House, then maybe. But I still think it would be a good idea for PD to come up with something entirely different tho that would really set it apart from Forza. Maybe something like PD themselves do an auction, make it a one of a kind car or paint scheme where the winner of the auction would really have something rare...with no way of duping or gifting it. Don't know how well that would work, but you see what I mean.
Another reason I said it wouldn't be a very good idea is because this is PD we are talking about. I'm sure they would find some way to muck it up,
EDIT: SlipZtrEm CONSOLIDATION WAVES
And that's sort of where the issue rears its head; without tighter surveillance of the community's save files, an Auction House could create massive problems.
And that was my initial first thought and also why I thought it would be a bad idea. PD doesn't seem to have as tight of security as T10 does. I could just see it turning into a big mess.