Way too soon for me to tell right now. But just pace wise, NSMB Wii could be over 15 million by the middle of 2010 so it's gaining ground fast. Even more than likely NSMB wii could be at the 20 million mark by this time next year. That's just something to think about when looking at this. But it's not like Mario Kart Wii is going to stop selling. My guess is another 5-6 million in sales in 2010.
I guess all that really matters right now is the longevity of NSMB Wii over a long time and I don't think that is something to worry about, especially if NSMB DS is anything to go off of. Seems like this NSMB Wii will be a game picked up with the system for a long time to come and selling to more gamers throughout the year.