This might have to come with a lot of Openbox (Waybox?) hacking to make work properly, but HiDPI monitors suffer on Lubuntu. Openbox doesn't have scaling support and we don't have the GUI tools for it.
Ideally scaling would be automatic.
I put in a community funds request to get a HiDPI monitor as I currently lack the cash; if I can't get the money for it, I'll have to shell it out myself. :/