In my opinion, the probability that we will see a new console from the console manufacturers by the end of a year are as follows:
2009: Microsoft- 0% Nintendo 0% Sony 0%
2010: Microsoft- 33% Nintendo 0% Sony 0%
2011: Microsoft- 66% Nintendo 33% Sony 33%
2012: Microsoft-100% Nintendo 66% Sony 66%
2013: Microsoft-100% Nintendo 100% Sony 100%
Edit: I just wanted to add that a console (namely the next XBox) being released in 2010 would have to be decided immediately, and would depend heavily on how it performs at Christmas. If the XBox 360 continues to chug along through 2009 and third party publishers continue to heavily support it I expect Microsoft will hold off on releasing another console.
Nintendo and Sony are both going to wait for someone to start the next generation because Nintendo has no need to start the next generation (at this point in time) and Sony can't be seen as having the most expensive console with the shortest lifespan.
