Jokes apart, Wii just needs some other big games to persuade the remaining potential users still in doubt, but fine with the current price. Then it will need a price cut, down to $150 for the basic unit, $170-180 for the bundles less costly to build and $200 for the Balance Board bundle. Finally, in its late years, after Wii2 release, it could still thrive priced at $100, $120-130 and $150 respectively, and maybe it could get then an all inclusive bundle with WS, WSR, NSMBW, MKW and Balance Board at $200-220. These phases could give it another 5-7M plus another 15-25M plus another 10-25M, it will depend also on new games, and, the final phase, on how long Ninty will keep it alive. Anyway, it could sell from 115M to >140M lifetime.
My previous prediction before it started having big drops outside of Xmas season was, IIRC, from 140-150M easily, to 180-200M putting a lot of effort into it and doing almost everything right.
Let's not forget, though, that any console surviving enough to meet the growing purchasing power of emerging countries' middle classes could end up selling lifetime several tens million more than the average predictions. If this gen won't do it, next gen most probably will, but when priced a lot lower than at launch, years later than this gen could, and it would be a big waste and missed opportunity for the industry, so I'm persuaded it's in MS, Sony and Ninty interest to keep alive this gen's consoles long enough after next gen begins, if this very profitable goal appears at reach.