For some reason I've seen a bunch of forums posts and emails about new Exchange Server 2013 deployments in the last week. The timing is notable, because Exchange Server 2013 has entered the “extended support” phase of its support lifecycle as of April 10th (a few days ago).
From Microsoft's announcement:
With the transition of Exchange Server 2013 to Extended Support, the quarterly release schedule of cumulative updates will end. The last planned cumulative update for Exchange Server 2013, Cumulative Update 21, will be released in June 2018. Microsoft may at its discretion release a future cumulative update to aggregate previously released critical updates or to address unforeseen future O365 Hybrid connectivity requirements. At this time there is no explicit plan to exercise releasing future cumulative updates.
So… that's the end of Exchange 2013 feature development. It hasn't received significant new features in a long time anyway, but the transition to extended support pretty much seals the deal. If you're on Exchange 2013 today, make sure you update to CU21 when it is released in June so that you can continue to receive security updates during the extended support phase.
If you are planning a new Exchange on-premises deployment today, you should deploy Exchange Server 2016. The exception would be if you are still, for some reason, running Exchange Server 2007 in your environment. In that situation, an Exchange 2013 migration must be used as an intermediate step to Exchange 2016, because Exchange 2007 and 2016 can't co-exist in the same organization.