That really depends on the flow of Kinect releases. If Kinect gets a lot of support it will still push many systems next Christmas season. If it doesn't it won't push a lot of hardware.
One important thing to consider is that we'll get new handhelds in 2011 so publishers will put more resources into the handheld market again after focusing on home consoles for the last two years or so.
With all consoles being on the market for 4 full years now and both the Playstation 3 and Xbox 360 having had their redesigns already (which pushed hardware a lot in both cases) I wouldn't expect hardware sales for any home console to increase in 2011.
Sony and Microsoft both will have to focus on increasing profits considering they've lost a huge amount of money during the last years and if they don't post profits now their business decisions for their next consoles could be limited. Losing billions of dollars and then going out to your investors and say "and now we'll just do that again!" doesn't sound like a good idea to me. Actually the Playstation 3 was still one the worst business decisions I've ever watched a company make from a financial standpoint. And I wouldn't expect Nintendo to drop the price to less than 150$. More than a 50$ price cut for any console doesn't sound realistic.
Considering these things and the fact that Nintendo seems unwilling to put any kind of effort into pushing the Wii besides bundles (Redesign? Price drop? 10 million sellers like Nintendogs for Wii? Tomodatchi Collection Wii? Super Mario Bros. Wii 2? Bundling Wii Sports Resort with the console in Japan?) I'd generally expect sales to drop from this year or maybe stay flat. But who knows, maybe Nintendo will go all out next year after focusing resources on the 3D in 2010. They definitely have enough options left.
One thing to remember is that just looking at current sales to judge the future selling potential of any console is quite stupid. Whenever we've seen a full month of either high or low sales for any consoles people always jump to conclusions and claim this is what the console will sell for the rest of its lifetime."Console X has sold extremely well / bad over the last 5 weeks therefore it will sell great / bad forever!"
In terms of sales potential and options left to increase demand (price cut / redesign / colours) the Wii still looks best out of all 3 consoles. We can't judge the potential sales of the Wii by looking at the first 10 months of 2010 because the console really didn't get any kind of support besides Mario Galaxy 2 and that was the 3rd Mario game on the Wii and the second 3D Mario so it didn't push hardware. Now, with a steady flow of releases the Wii is selling extremely well again.
In terms of actions taken to increase demand (i. e. fully realising the sales potential of the respective console) I expect Microsoft and Sony to at least match Nintendo by reducing prices (not by 100$ though) and pushing Kinect and Move. But again: Nintendo could potentially put some of its resources into the Wii again after having to focus on the 3DS this year (developing the hardware and software - next year they'll just have to focus on software and with the 3rd party support the 3DS is getting Nintendo shouldn't struggle to keep sales high). Especially a redesigned Wii would make sense and could push millions of additional systems.
So basically sales should be either flat or down for each console. Something like this:
12 - 17 million Wii (high sales potential but weak "support" by Nintendo)
9 - 13 million Xbox360 (not going to be down by more than 30%. Up only if Kinect gets very good support)
9 - 13 million Playstation 3 (again not down by more than 30%. Up only if Move big Price cut)
We could see all consoles selling less than 15 million units next year.
Edit: Just to make this clear, the higher numbers only apply in case a company pushes the system a lot. For instance the Wii has a high sales potential but going by how hard each company pushed their console in 2010 the Wii would come out at the lower end of the prediction and the HD consoles at the higher end if things don't change in 2011.
