When I start 0AD the screen is all but unreadable.
My eyesight ain't what it used to be, though my 3840x2160 screen works great when stuff is scalable, but when everything is dimensioned by the pixel I'm screwed.
I managed to find a settings button, but I couldn't find any settings that would let me change the resolution, or - better yet - set some arbitrary scaling factor for UI elements.
I assume this means it would be unplayable, but to be honest even the tracking down the settings screen was hard enough that I gave up at that point :-(