I'd be willing to bet at NAB, or an announcement at NAB of the release of any new revisions.
And just my .02 on the next version...
if the last few years has been an indication, Sony will release the next version at IBC (though I could be wrong). They did NAB a couple versions ago, then they did IBC a year and half or so after that release, and then they did NAB a year and a half or so after that (that was NAB 2009), unless my memory is failing me, so if that keeps up, IBC 2010 would likely be the next version of Vegas Pro.