The Wii is around 98 million whereas both PS3 and Xbox360 are low 70s million. PS3 sold about 11 million this year and Wii sold around 5 million this year. The Wii sales should drop even more with the WiiU out. Depending on when the next gen consoles are released, both Xbox360 and PS3 should sell another 11 million this year (give or take 1 million or so). PS3 and Xbox360 could still sell moderately better than the Wii few years after the respective PS and Xbox next consoles are released (if there is a good price drop after the next gen consoles are released). Maybe in 3-4 years, can Wii be knocked from the 1st place console sales for this gen?
I think the PS3 has another 3-4 solid years ahead of it. Even 360 if MS doesn't abandon it.
Actually wouldn't surprise me if PS3 outsells the Wii U for several years. Lower price point, cheaper games, far bigger library, Blu-Ray playback, PSN, larger install base to sell to for devs, similar graphical fidelity, etc.
Especially wait till you have $179.99 and lower SKUs on the PS3 as a standard.