Well, I think Nintendo need to start out strong with their next system.
Having both a 3D Mario and a new Metroid at launch would be smart to gain early adopters. If not at launch they could space them out a little bit, make sure they hit in the first year though. They could then follow up with Mario Kart, Animal Crossing and or a Splatoon sequel in year two.
Their teams are likely already working on the next system, the time frames could line up fairly well for a strong opening year.
Also, putting at least Metroid out at launch would probably give it the best chance to sell the most units, as we discussed.