Wii is already outselling PS2. When will PS2 resurge and take the crown is the more accurate question here.
A few other general points for the thread...
1) Despite never attaining over 50% marketshare, the Wii is still by a decent margin the fastest selling home console in history, both in hardware and software. Trying to tie longevity to marketshare is misdirected, faulty and easily historically disproven anyway. GBA had a far higher marketshare figure then DS, yet I doubt you'll find anyone who considers the latter to be the weaker competitive platform with a less optimistic later shelf-life.
2) It's also a flawed argument that 3rd party support is necessary for a competent platform wind down. Again, GBA makes for the most relevant recent touchstone for how a successful Nintendo system with mediocre 3rd party support can be brought to a soft end on the strength of 1st party commitment. PS1/PS2 aren't comparable as Sony's never had the 1st party strength and brand Nintendo does. N64/GC aren't comparable as they never had the market success and presence Wii does. GBA really does make for the best recent comparison, and holds quite a few parallels with Wii actually.
3) Nintendo did lower production in early 2009 and are now again suddenly faced with extreme regional supply constraints like the platform hasn't faced since 2007/2008. Amazing what a legitimate killer app (that was dismissed by pundits beforehand) and minor price drop (first since launch even!) will do for you. Not exacting the sign of platform that's downward trending if you ask me. ;)
