This is just a theory, but I believe that one of the "HD twins" are going to die off very quickly. Both consoles are redundant and are being marketed to the same shrinking audience, so a crash in one of them is coming. The Wii has locked up the "expanded audience" so tightly that Microsoft and Sony can't touch them, and the Nintendo core audience for the most part is disinterested in the HD twins.
I predict that the HD twin that will die will be the Xbox 360 mainly because of RROD. Sony at least has a huge brand awareness remaining due to their domination of the previous generation, so the possibility that the PS3 will die off quickly is unlikely IMO (but it can happen). Only time will tell if I'm right.