X360 is expected to end the year anywhere from 2.1 (current gap) to beyond 3 mill. But lets say for arguments sake 360 does 2.4M in Dec and Wii does 1.8, pessimistic and optimistic in respective order, if estimates and general opinions go (Wii can be anywhere from 1.5 - 2, X360 2 - 3).
Going back to my pessimistic estimate, that would mean the X360 ends the year at 2.7 ahead of Wii, with Wii ahead lifetime 6 million.
That means the Wii is down 1.8M YoY and the X360 is up 1.2m~. The guy on Gamasutra, and I, and a fair few others believe growth in the U.S for the X360 is a very real possibility if MS play their cards right. It's clear Kinect didn't peak last holiday now, and it's done swell again, without a price cut and, tbh, exciting new SW either. It did have retailer deals along with everything else this BF though. Next year a nationwide $149 X360 and $99 Kinect (along with the much cheaper bundles) will do very well. It's hard to see them being down anything more than 1 mill. I believe they held off on a price cut this holiday because:
A) They knew the Kinect was still hot, and didn't need a cut to either platforms.
B) Next holiday will be tougher, with WiiU and PS3 going $199.
So they've saved their cut for then. If the rumours of another redesign are true, along with Halo 4 and possibly some actual real HW selling Kinect games (and that's certainly not a certainty, but you would hope...) along with a cut on all HW, then they would would be up for the holiday season enough to offset the declines during the first 8 months.
That said we have Kinect Star Wars, Alan Wake AN and Witcher 2 coming in the first half. Whilst none bar Star Wars will shift HW, it does show they're not ignoring the first part of the year like they did this year. Hopefully this is a sign they're going to push for sales all year round next year.
The Wii ... Its non holiday months are getting so low it's going to be hard for them to lose much yoy in raw units. That said they did push 200k+~ most months of the year. Who knows if the price cut did help them after May, perhaps if they hadn't cut sales would have been down quite badly. Will they cut again in May? Can they fesibly do this in their current state? They'll be celebrating their first ever Fiscal Year loss, 3DS isn't making money, and WiiU is on the Horizon. If they do cut I think they're insane, which is why I don't believe they will, at least not until the holidays. But even then, going up against a $199 PS3, a $149 360 and cheaper Kinect bundles, the WiiU (which is what Nintendo will then be focussing on), and no new SW, Wii has the potential to be down a fair bit next year, price cut or no price cut. Even with $99 wii deals it couldn't beat PS3 this month - barmy!
So as a range I expect X360 to be 6.6 - 8M in 2012 and Wii to be 3.8 - 4.2. So 7.3 for X360 and 4 for Wii, closing the gap to 2.7 end of 2012.
Put me down for September 2013.