I'm optimistic that it will get better as more developers buy newer laptops with QHD+ resolutions. ElementaryOS even had a pledge fund to get the founder a 3200x1800 res laptop just so he could actually dogfood his OS on a hi-res laptop and improve HiDPI support. Unless, of course, the average Linux developer remains a graybeard with a Thinkpad. Then we might be waiting for awhile. :)
The other major hump to get over at the moment is that many of the distros are spending resources to switch to Wayland, and I imagine we'll need to let that transition stabilize first before we get the bulk of resources diverted to HiDPI support.
The Wayland transition will, itself, probably leave people with my preferences (tiling WM, a stack of other small customizations that depend on X) high and dry for a while, but I guess one can hope that it'll be a solid foundation for future development.
I'm just not transitioning until my preferred WM (stumpwm or another Common Lisp tiling WM) transitions. I'm a bit skeptical that Wayland provides any significant benefits for my use cases.
The other major hump to get over at the moment is that many of the distros are spending resources to switch to Wayland, and I imagine we'll need to let that transition stabilize first before we get the bulk of resources diverted to HiDPI support.