@Carl: As indicated in the post:
We expect the next on-premises version to be released according to our traditional release cadence (2-3 years after the previous version).
We'll share more details as we get closer to release.
Note, this post listed some of the usual questions we get around this time
(When's SP1 coming? When's the next version coming? What's new in the next version?), followed by an unusual one
(will there be another version of Exchange Server?). This post addresses the latter question.
http://blogs.technet.com/b/exchange/archive/2013/11/20/exchange-server-2013-service-pack-1-coming-in-early-2014.aspx shortly
after this post. http://blogs.technet.com/b/exchange/archive/2013/11/25/released-exchange-server-2013-cumulative-update-3.aspx
Exchange 2013 CU3 was also released shortly after that.