The concept of 4K TV broadcasting is only just getting off the ground, but its overseers are already planning for what comes next. The Ultra HD Forum has published its first "Phase B" guidelines detailing what companies should aim for with future 4K broadcast tech. Not surprisingly, high frame rates should play a major role -- the group is hoping for 100FPS and 120FPS video (depending on the region) with a fallback for 60FPS. It's also pushing for dynamic HDR video through formats like Dolby Vision and SL-HDR, while Dolby AC-4 and MPEG-H would provide audio that could adapt from elaborate 3D sound setups to a plain set of headphones.
All these additions are going to hike bandwidth demands, but the Forum is betting on Content Aware Encoding (where encoders reduce data use in relatively stationary scenes) to lower the requirements. Providers and broadcasters that can already handle 4K TV might not have to plan another upgrade just to adopt high frame rate video, especially if their content involves a lot of still shots (think golf or talk shows).
This is a set of guidelines, so it's going to be a while before you see TV providers and equipment makers rolling out the hardware and services needed to make this happen. Your brand new 4K set won't be obsolete for a while yet. However, the Forum's criteria gives you an idea of what you can anticipate in the years to come.