Please make Blender capable of automatically recognize the Linux desktop PPI, and set it to its interface accordingly.
Even though X11 has a DPI setting for the viewport, it seems each desktop environment/widget set uses its own scaling. see: http://www.makeuseof.com/tag/linux-hidpi-support-for-gnome-kde-xfce-cinnamon-and-firefox/
- Read the DPI settings from X11 and guess, while this should work, it seems nobody is using this setting to scale the UI, so likely its not a reliable value.
- Read the interface scale setting from gnome/kde... etc (not very portable).
However it would be good if there was some more straightforward way to get this information from X11/xlib.
The most generic solution might be Xft/DPI from XSETTINGS:
This is mostly a GNOME / GTK thing, but from what I can tell this is what Chrome and Firefox use (though GTK) on all desktop environments. It should also work with KDE through xsettings-kde and Xfce through xfsettingsd.