if I could pick?
a Mario Galaxy and F-Zero installment. I think that would gurantee the system's success
seriously if they have a fairly regular controller and Mario Galaxy when the NX launches then the system will do great. I still constantly see people on like Twitch streaming Mario Galaxy, people love that series
if they wanted to gurantee success launch with a Mario Galaxy game and a console Pokemon dedicated game (an updated Pokemon Stadium!!!!)
knowing Nintendo lately though they'll probably launch lacklusterly with like a 2D Mario and Pikmin :/
personally I would love to see F-Zero revived and a new 3D platforming IP (sorry Splatoon, but you didn't really fill my new IP niche craving from Nintendo)