From All About Microsoft:
Instead, the company will focus on rolling out new features for the online versions of those products, which are the core of Office 365, this year. And in 2015, Microsoft will deliver new on-prem versions of those two servers, according to Jeff Teper, the Microsoft Corporate Vice President of Server Services.Microsoft: Next Office server releases not until 2015
I had been thinking Microsoft would deliver next Office servers this year, given that the company has started its Exchange Technology Adoption Program (TAP) testing program already. Clues about a new version of Lync Server coming later this year also made me think the next Office server wave (codenamed "Office 16") would arrive in 2014.