This all depend on when the new wave of consoles come out. Well i think it will come 1st in the end, my reasons for this is when everyone realises the ps wands can do pretty much everyhing the wii remotes can do but with better graphics(if sonys software is up to scratch) the wii will look outdated so they will be first to bring out a new machine maybe within the next 2-3 years also they are the only one who is in any position to bring out a new console(MS could do but thats just throwing money away not that they haven't got it to throw away). Wii people might be looking for an upgrade before the new wii comes out.
Then we have the 360 which is already starting to look outdated and falling behind the PS in hardware sales (since redesign/price drop).I can't really see what MS has up there sleves to counter this. Natal?im not too sure about. (Just looks like a pimped PS eye) good games but so does sony. So i can't really see the 360 being too much of a problem to overtake and im thinking will be about 4 years untill MS bring out there new system(wanting to recoup some losses) sales will drop off even more by then.
these are just my thoughts please dont skin alive im new :P