Hello! This looks really nice, but I'm using two 4k monitors. At 200% the text looks blurry, and at 100% everything's really tiny. I don't know if higher-res UI is on the cards, but if it is then this is my throwing my vote in for one!
That's a very very edge case and unfortunately I'm unable to test the UI in these conditions since I just have a 1080p monitor. ^^ You could always try editing the sizes and adapt the theme specifically for your hardware, it's pretty easy once you get the hang of it.
Just to add more info: what you need to edit is the theme.xml file and is under the <dimensions> and <font> tags. I guess you'd have to double or triple the values to make sure everything is visible in a 4k screen.
As for the icons you could try upscaling the image sheet.png by 3x or 4x using nearest neighbour as scale method. ^^
Good luck and if you end up managing to do something you like, please share with us, I'm sure there are people with similar setups that would be happy!