There's a test service in Europe run by Eutelsat. This is using current compression and modulation systems - and uses 4 x 1080/50p streams at 10Mbs each to broadcast 4 quarter-screen images that are merged into a single 3840x2160/50p signal.
So it takes up 4x the space of regular HD services, the best part of a full transponder. But it is on-air now.
H265 compression should improve this significantly.
A number of European and US broadcasters are trialling 4k production - and a number of 4k capable OB trucks are due to come on-stream soon. The UK's main Pay-TV provider has shot and screened 4k sport coverage.