I think that would be a great idea as long as it is realistic especially since most of my mtb friends have a ps3 or xbox 360 there would be quiet a bit of sales
I think with the World Cup race circuit growing in popularity it could be based on that with all the different tracks and a career mode where you could choose a team, customize your bike etc.
Aswell as the whole freeride side of Mt Biking now
...signed it EDIT: if someone could come up with a game engine of SKATE, but with MTB/BMX and you could cruise around the street but also take a trip to a mountain for some downhilling... now that would be sweet
It won't happen, there's too many variables to even think about producing a halfway decent game. Maybe bmx as the ground is normally smooth but forget about a downhill one.