Thanks all, for the information and comments.
Indeed, I can imagine that it's a fairly large workload to develop and maintain multiple res UI's, under the current (and updated) working model.
Frosty - thanks for the heads up.
Given your information (which by the way is very pleasing!) it kinda creates a catch-22 for UI modders. In that if some development is being applied at your end towards realtime scaling, the artists here probably won't begin the large investment in their time creating multiple res versions. But at the opposite end of the argument are the users, who won't benefit from having appropriately scaled hotbars etc.
Therefore, is it possible to implement the realtime UI scaling code on Roheryn? Perhaps at least then your development could be aided by the efforts of a community such as this?
Just my $0.05..