Probably the easiest way for them to go HD is to license Microsofts Xbox 360.
Its a simple architecture with a well developed toolset so they don't have to go through the pains of multicore architecture development.
Take one Xbox 360 architecture, stick the name Nintendo on it, call it a day and or If they want to give it a bit of a spruce up, they just have to increase the ram to say 1gb using 4 high density GDDR chips running at 900-1000mhz and perhaps update the CPU a little and tack on another core which will help them run their UI a little better.
Tease.