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.
