Word on the street is that AMD will have a new revision of its GCN "Hawaii" (aka Radeon R9 290 series) architecture ready by early 2015. The revised GPU will reportedly be made on a mature manufacturing process so it's most likely 28nm.
If you wan't AMD's next-gen graphics you'll have to wait until Summer 2015 for the arrival of Caribbean Islands, a new architecture that is expected to be made on a 16nm or 20nm process.
The launch window for Caribbean Islands is subject to change at this early stage, of course, though a launch between June to August is most likely. Other details about Caribbean Islands graphics cards, such as whether they will make use of a 16 or 20nm process, are not known. AMD may reveal more information during its investor relations conference in February 2015 but between now and then the descent into the speculation quagmire begins.