sky don't have hdr yet for the premium customers , so they need to fix that first.
For 4K sport sky were (still are?) luxuriously 30Mb/s off of satellite, so should be better than streamed BT 15Mb/s, but sky don't seem to legitimately advertise - we are the best
Also, for 4k movies, I don't know if sky has same delivery system as other streamed providers ... they have a big skyQ box, with lots of ram and buffering capability, so may not have capability to deliver 4k content to a less hardware capable atv/nowtv box.
Nonetheless whether the additional installation/maintenance cost of satellite in sky infrastructure has a long term future, versus fibre into the home ... so I can see sky re-branding as Earth ?