1) NO
Because I don't have high-res screens
2) NO
Answered above
3) NO
Not in the near future.
I personally don't even get to 1080p at the moment, I am still using three 1440x900 monitors.
Pretty positive I won't be upgrading to 4K within the next 5 years at least, unless I happen to win the lottery
4) YES
It would reduce eye fatigue and help with the workflow as you can fit more stuff into your screen, which is the reason why I use multiple (very cheap) monitors to work around the issue as a low-cost solution.
Anyway I'm totally in support of 4K optimization to make the product more competitive, since 4K is inevitably and exponentially increasing.