multicast is already here, but 4k is not the answer you were looking for
I dunno about other ISPs, but talktalk use multicast for all their 'extra' youview channels, so that bit of technology is already in the bag.
My real issue is that from a perceptual point of view proper motion tracking and handling is far more important than more (than existing full HD) pixels. Even 50 or 60hz prgressive scan is still going to mean everything going blurry as soon as it moves, just like it does already, so 4k stuff is going to give a far bigger improvement to costume dramas than sportsy stuff