Iwata said the only reason Wii is not HD capable is because the market penetration was not high enough at the time of the launch of Wii. They've pretty much all but confirmed HD in their next console. What will be interesting is watching when their dev teams slow down in Wii development as that will give us a hint as to when the next console will hit.
Another interesting thing to look at will be the controller. Nintendo ALWAYS upgrade their controllers in meaningful ways.. I mean look at the difference between the NES, SNES, N64, GCN and Wii controllers.. You couldn't place them all as Nintendo controllers if they didn't have branding. They're all completely different designs and I'm sure their next controller will follow that pattern







