It is well over a year since getting a 4k monitor. In that time we have gone from Windows 8 to 10 and a couple of updates. In the end I settled on 150% scaling. So not quite full retina in Mac terms (200%), but actually this is the correct DPI setting for a 32″ 4K monitor. An A4 page at 100% size in Word, for example, really is basically full size (and I can fit multiple on one screen!).
In general for how I am working there have been a few minor improvements in that time. In Windows 10 the switch to HiDPI and scaling has gone forward, but a bit roughly. Of course all the UWP apps (Metro) work out of the box, but app support has been pretty spotty and takes a long time.
Of the apps I use most things like Sublime Text made the jump quite early as had Firefox and Thunderbird. Spotify did eventually, and then most recently Evernote. Lightroom now looks and works mostly ok, nicely scaled UI elements with full resolution images. The laggards now are a handful of older apps that probably never move, anything from Apple, plus of course Steam. Although that just means they are fuzzy, but full sized. Rarely now does an app claim to support scaling and then not do it, resulting in a really tiny window.
The real rough spot from comments online seems to be support for multiple displays at different scaling, or switching displays. But I don’t suffer either of those since this is a desktop PC with a single monitor. Of course that was one of the reasons for getting this display in the first place.