One thing to remember with the Wii in predicting hw for NSMB to tie to is how long it has taken lesser machines to decline.
N64/GC were still at 30% and 40% respectively of their peak fiscal year three fiscal years later and thats without significant third party support.
April 1997-March 1998 N64: 9.42m
April 2000-March 2001 N64: 2.85m
N64: 225m SW Market LTD, 18 third party million sellers life time, only four of which cleared 2m. One of those topped 3m in 6 years.
April 2002-March 2003 GC: 5.76m
April 2005-March 2006 GC: 2.35m
GC: 208m SW market LTD, 15 third party million sellers life time - only two of which cleared 2m in 5-6 years.
Wii: 26m peak (April 2008-March 2009)
Wii Peak *35% in March 2012 Year... 9.1m Wiis shipped worldwide
I don't think it will decline that fast though. Through December 2009 we have something like this for Wii:
Wii: ~516m SW market LTD (shipments - I'm estimating), 45 third party million sellers lifetime (VGC sellthrough), 10 of which topped 2m (~3/year). Five topped 3m, one has topped 5m...and this is in half the time N64/GC were on the market. So even when Zii, PS4, X720 are introduced, Wii should continue to see fairly ample support from third parties - slowing its declines.
It isn't going to do 6m-18m-26m-20m-16m-12.8m-10.2m and then behave like N64 did and drop like a rock. The tail should be rather long as the fanbases for the successful third party companies will still be active on Wii. Rather than selling 27m from April 1997 to the end of its lifespan as N4 did after peaking at 9.4m in the first year Wii will probably decline more softly and add ~32m-36m starting from its last 10m+ year.
People are difficult to govern because they have too much knowledge.
When there are more laws, there are more criminals.
- Lao Tzu