I bet that by the end of 2015 that there will be special events shown by BDUs in 4K, not unlike HD 15 years ago. It may even happen sooner - apparently the World Cup this summer will be shot in 4K, or at least some games will. Perhaps the entire 2015 Superbowl will be in 4K. Maybe some BDUs will start to think about providing this content, but I guess the first issue is that they have to give their customers STBs that can (1) receive a 4K stream from the head end and (2) output 4k resolution over HDMI.
Don't forget that there was an ESPN 3D channel that is now shut down. Before too long, and maybe even before all channels are in HD, we will start seeing 4K channels - TSN-4K.
But I really think that Broadcast is being left behind, it certainly is far different from the early days of HD 10-15 yrs ago.