Wii Relax -- Definitely going to get to 15m+ because it's targeting the audience that made the Wii successful in the first place... baby boomers
Super Mario Galaxy 2 has a chance of just barely touching 10m. Perhaps NSMB Wii's success will influence this one in a positive way.
NSMB Wii - Will get another 10m added on to it's current 10m.
Edit: Also, in terms of what Nintendo can release:
Wii Fly (aka Pilot Wings with a new name)
Wii Play Online w/ bundled M+ controller
Pokemon MMO