The biggest problem in linux is not directly HiDPI.
HiDPI works (mostly).
However if you can't use wayland you will have a problem when you need the following:
Multiple monitors with different screen resultions.
Lets say your laptop has 4k and you use two external monitors with 1080p than it gets tricky with older wayland or x.org.
However on later stable/edge channels most things are probably better than when I tested this and I even have a colleague which has a 13" xps with ubuntu which works pretty will with its docking station.
If you have a good GPU you can use the xrandr commandline tool to set up display scaling, so your secondary low-DPI screen is rendered at high DPI and scaled down. Then you only need one DPI setting for your DE.
Well, it‘s good that it „could“ work, however i expect it to work without searching the Internet for xrandr configs. (And as said newer Weston/Wayland work way better)
However if you can't use wayland you will have a problem when you need the following:
Multiple monitors with different screen resultions. Lets say your laptop has 4k and you use two external monitors with 1080p than it gets tricky with older wayland or x.org. However on later stable/edge channels most things are probably better than when I tested this and I even have a colleague which has a 13" xps with ubuntu which works pretty will with its docking station.