the real question, as I see it, is not whether the 360 will remain a viable platform, but, rather, will MS have to destroy the PC gaming market to enshrine the 360 (and future Xbox generations).
and that is a very good question. one of complaints we keep hearing from people is that Sony has exclusive titles while Xbox/X360 titles are "PC copies". Well, then the answer is more titles that can only run on the 360. They are already moving in that direction with the Mass Effect trilogy and other games.
if the PC gaming market is destroyed, then occidental-style games will migrate to the Xbox-type console first.