I understand this is probably very low priority but here it goes This is how things look on my 14" (3200x1800) laptop: http://i.imgur.com/5agtodL.jpg I swear it's unreadable in RL, hehe.
HiDPI support is not specific to linux and according to http://feedback.unity3d.com/suggestions/support-retina-resolutions-in-th work on it is already ongoing.
Yup, I only have 1080p on 13-inch laptop so not exactly super high dpi, but I still would benefit greatly from having scalable ui.