I'd say sometime 2013 just for the announcement to be honest. This generation is just now beginning to peak, so they aren't going to pull out anytime soon. Companies are JUST NOW learning to embrace the technology of the PS3 as far as development goes and with new peripherals being released there will be more room for growth. 

Nintendo will start rapidly losing market share to the PS3/360 throughout 2011 and will start development on their next-gen console rather soon. MS/Sony will hang in there for roughly ~3 more years. They may both begin various development processes as far as deciding what type of hardware they want to use and at least set goals as to an architecture outline. MS will start to search for other forms of disk media to write games on, and Sony will probably either continue to use Blu-ray or release a BR2 (different name, obviously) that basically uses the same format as BR so it can be read by current players, but has a higher capacity.

I personally think both of the next-gen consoles from Sony/Nintendo will start to further ascend into the realm of PC hardware formats, kind of like they've done this gen utilizing standard 2.5" HDD (yes MS does it too, and installing a 2.5" HDD isn't much harder than doing it in a PS3), USB 2.0, and a more advanced operating system.

All-in-all, this generation is far from over for MS/Sony. Nintendo will jump the gun on development as their market share starts to rapidly deplete with the Wii. MS/Sony are just beginning to peak (2009/10/11 are all going to be GREAT years for them) and will ride out the current gen until they've at least hit ~30% market share each.

I reckon the ps4 will release in 2016-2018. I think the xbox720 will release in 2012 ansd the super wii but instead of releasing a new console sony will compete with the ps3. i.e reversing the situation this gen, where sony have the less powerful, easier to develop console with a masiive install base. That way sony could buy lots of third party exclusives and finish off microsofts next bot even before the ps4 releases.

2012-2013, about one year after Wii2 is my guess.

Super Wii will likely release late next year. Maybe in Japan only, maybe Worldwide.

Xbox 3 will probably release 2012 Holidays. Would be perfect for it. Would give them enough time with Kinect and enough time to drop to $150/$100 with the 360.

...

PS4 should be a simultaneous launch with the Xbox 3. I pretty much expect them to be equal on the power, and I expect Sony to want to get those easy 3rd party ports again, at the same time not letting MS have that critical 1 year advantage. PS3 will also have been given enough time to reach a mass-market pricepoint, cut into those massive losses and will have probably peaked in sales during 2011. I expect the majority of big franchises to be available on launch, or within a year of launch and come packed with a DualShock 4 AND a new PS Move-like controller option. Will cost no more than $400.

oh shit, i like that, havent heard or seen anyone say it like that makes sense to call it that though

i still say 2014 at least for 360 ps3 why would they release natal and new slim if new box is coming in 2012? as for sony i believe they still got alot left in them SW power wise and there console is still $300 wasnt that ps2s launch price look how long ps2 lasted after that $300 price point

I think Sony and Microsoft will probably play 'chicken' with each other for a while

I think Sony and Microsoft will probably play 'chicken' with each other for a while, neither want to release a new console, because they have both barely started earning back their investments. Microsoft spent a lot of money through the original Xbox and now Xbox360 cycle and Sony burned a ton of money on the PS3 launch.

Also I think they both want the other to make a first move and then try to release just shortly after with a console that offers some features that makes it easy to make superior multiplatform games on their platform, like some graphics effect for 'free' through hardware. Sony especially don't want to go another gen with the multiplatform games being marginally worse on their platform, instead they want every review to say 'if you get PS4 version it is a bit better than the Xbox720 due to the XYZ stuff'

Of course Nintendo might force both of their hands with their new console which I think will come earlier.