It’s a bit like some conspiracy theorists claim 650b to be. Sony are massively pushing 4k, both getting cameras into studio’s and TV’s into houses because they want people to upgrade their TV’s.
It seems that a lot of photographers shooting video for commercial use are shooting in 4k. I was down on the Somerset Levels earlier in the year, to see the starling murmerations, and there was a bloke with a very whizzy camera on a tripod. I went over to have a closer look, and it was a RED modular camera with a Canon DSLR lens on the front. He was shooting 4k for a documentary he was putting together about the starlings. Storage was a bunch of SDXC cards arranged in a RAID array, either 32 or 64Gb, I can’t remember for certain. He was from Devizes, and not from a particular station like the Beeb.
The new Sony A4s DSLR mirrorless camera can shoot 4k up to ISO 406,900, but requires a separate recorder pack to do so, I think because of heat issues, the results in almost complete darkness are astonishing.