...and why at that time?

I think late 2013/early 2014 we will see either a new console from MS or Sony. Most likely MS though.

If I were Sony or MS I would forget about the 'console war' for a while and not hurry the next console. Now that WiiU is announced they don't have to worry about Nintendo leap frogging them in the hardware race. I think on a graphical side (although we don't have clear specs) PS360 and WiiU are in the same league, with WiiU edging out the competition.

Where innovation is concerned, Sony could also pull of some tablet action across PSVita and PS3. Next to that they also have PSMove. And they are finally making money on PS3. If I was Sony I'd put all my money in making great games, if they keep supporting PS3 for a couple of years the user base could grow to 100 million. Why bring out a high-tech successor and start from scratch making huge losses like PS3 did?

Same goes for MS

Graphics wise their console is fine. Casual players have no desire for high-end graphics.
MS is making money on their console, the user base is growing steadily, games are selling extremely well on that platform.
It's the leading dev platform (and probably still will be when WiiU arrives) and Kinect is selling like hot cakes.
There is no need to hurry a new console.

I think the next three years will be very profitable for all three platform holders.

I think it depends on the sucess of WiiU.
If it flys off shelves like the Wii did and 3rd party jump on this time, 2013/2014 is likely imo.
And more likely is 2015 for XB720 and PS4 at 2016, if you ask me.
Ninty should make the WiiU at least 4 times the power of PS3 and streaming possibility for 4 tablet-controlers, but as far as i know Ninty, they won't do both things.
That's why i think 2015/2016

2015/2016 seems a bit late but I wouldn't mind, games and game developers will benefit from this.

Fall 2013 for both Sony and MS, with just reasoning.

-If Wii U launches in 2012, it will kill off a sizable portion of 360 and PS3 sales.
-a 2 year delayed release is a bit excessive for PS3 and 360. To be fair Nintendo tries to make their console not a competitor to the PS3/360, but it's own thing, but 2 years is too long.
-Call of Duty map pack exclusivity is limited to the 2012 Call of Duty. If the 2013 CoD is released on the 360, it will also be released for the successor.
-Most games, mark trilogies, 4th installments on 1 console probably won't sell well. Gears 1-3, Forza 2-4, Resistance 1-3, Uncharted 1-3, Mass Effect 1-3, and by 2013 there will be a Killzone 4.
-Since NES every generation has seen 3 Final Fantasy's. We are at 2 now.

However MS did announce a new Halo trilogy. My argument is that, who said this will be 360 exclusive? 343 promised a new Halo every year, but I'm not sure if there will be a Halo on 360 past Halo 4.

It'll probably be a couple more years, 2014 I'd say.