@Slamdunk We haven’t made or communicated a decision yet. However, all the latest RFCs have omitted the Interface suffix, including the now published zend-expressive-hal and zend-problem-details packages.
My own rationale for doing so is nicely summed up in this article from Mathias Verraes, where he argues that an interface, as the contract you are programming to, is a first-class citizen of your code. Implementations should indicate how they do so, or what context they do so for. While I’ve long been a proponent of the Interface suffix, when I consider developing the interface first, based on the use cases we need to accommodate, I find I agree with Mathias more and more.