Look at BD now, the 360 is losing support.  PS3 is getting exclusive add-ons and content that the 360 isn't.  Developers are limited by the DVD and losing interest and want to jump on the band wagon of the PS3's untapped resources.

And Sony isn't showing up to 3rd party studios with a suitcase filled with $50million to pay off studios to turn their back on the competition which is a tactic that Microsoft depends on in order to "compete".

I think the scenario is pretty unlikely. Sony have shown they can learn from their mistakes and come back and they have done so very successfully. I dont think they will allow the same issues to plague PS4. I read somewhere (maybe the PS4 thread) that when they develop the PS4 (if they arent already), they will try to improve it so that developers have a much easier time coding for it than they have for the PS3.

MS have been a mixed bag so far - brilliance with regards to marketing their exclusives with stupidity about the focus on FPSers and NA thereby missing the opportunity to dominate in Europe (Japan would have been a hard ask even with brilliant RPGish exclusives). They will need a blu-ray or equivalent to match PS4 is disk space.

I would say that Nintendo would be the wild card. I dont see them winning the next gen by just powering up a next gen console to PS4 or Xbox720 levels. I suspect something new with which to attract people with. And considering the money they must have made this gen, I think they will probably be successful