Let's see!
If we just go by the first week of sales in the year, here's the 2009/2010/2011 numbers:
Americas, week ending 9th January
09: 69,652
10: 52,300
11: 64,735
Others:
09: 87,888
10: 60,898
11: 68,263
Japan:
09: 22,093
10: 16,788
11: 21,141
WorldWide:
09: 179,633
10: 130,035
11: 154,140
So, just looking at that, 2011 is right in the middle of 2010 and 2009 in sales.
Here's the sales for those years.
Americas:
09: 3552k
10: 2236k
Others:
09: 3402k
10: 2382k
Japan:
09: 422k
10: 545k
Worldwide:
09: 7376k
10: 5164k
As 2011 is seemingly right in the middle of 2010 and 2009, I'd say 2009's sales are the high-end and 2010 are the low end sales. Mario Kart Wii needs 3970k to reach 30 million. How long did that take in 2009 and 2010?
2009: Sold 4266k by week ending 18th December
2010: Sold 3952k by week ending 5th September.
So, I'd guess between those two. Late November would be my personal guess.
It depends, though. How much will MK3DS boost MKWii?
