The Sky satellites are old tech, they were not made to carry 4K content, and can't easily be modified That might be easily solvable but then people don't always have the most modern boxes either. If people don't have the equipment to use the 4K signal they aren't going to pay for it. I wonder, despite the availability of high quality radios available how many people still listen to tinny awful ones? Same with DVD vs Blue Ray. It's a situation of is it good enough?
Sky get most of their money for the number of channels transmitted, not the quality of picture, so they aren't going to bother as long as they make a nice profit.
I'm surprised none of the rental companies tried offering a digital content on memory stick option. You would go in, get a stick, they put date limited content on for you. Next time you go back it's deleted and replaced with new content. Might have been interesting.
Not sure what your off about with the satellites.
They will carry 4k easily enough, as its all digital - bandwidth is the bottleneck & the price it costs them to pay Astra. I used to have a motorised dish & the picture quality across Europe was far superior to what we get in the UK - especially the German satellite - though now Germany is Sky as well, it has probably been compressed highly to save bandwidth/force more channels down the same bandwidth.
What you are saying about memory stick was an idea about DVDs years ago. The technology was called DIVX - Stores could burn a blank disk that would have an expiry date.
As you point out though, the biggest issue is the uptake of subscribers upgrading the receiver box.