This whole issue just seems so pathetic. PostScript and DPS, notably NeWS, have device-independent scaling from the outset - you can completely omit even mentioning pixels, even though they're 2D. Wayland braying on about scalability here just highlights how they don't even understand the game.
Going to OpenGL is a nice tactic, since OpenGL doesn't give a flip about screen coördinates anyway.
I miss NeWS - it actually brought a number of great capabilities to a window system - none of which, AFAIK, are offered by Wayland.