There are talks of using a newer codec to increase efficiency, but you are asking the golden question IMO. The reality is that 1080p isn't that good from these providers and 4K is marketing, not substance. You will get a 4K signal with 4 times as many pixels shoved down a pipe that can't handle 1080p properly. So, things may improve in some areas, but will take a hit in others. Video without a lot of fast action are likely to see improvement as backgrounds which aren't moving won't need to be redrawn quickly. So, more detail there. But, once motion starts, bandwidth needs to peak, and it won't be available.
4K is really going to need more bandwidth, and 4K Blu-ray Disc really can't get here soon enough IMO.