> So you are saying you would want one physical square inch on a phone to be the exact same size one square inch on a projector screen?
If they're not the same, then they're not inches.
If they're not the same, then they're not inches.
The current system of pts or inches varying by context would be like if an oven manufacturer said "Well, 60°F is pretty warm, and 90°F is downright hot, so we'll just recontextualize those numbers for our oven gauge. Bake cookies for 10 minutes at 80 degrees.
Unless you're using some other oven that scaled temperatures differently, in which case bake them at some other temperature instead ¯\_(ツ)_/¯
One could argue that you really are using inches, it's just that everything ever displayed on a screen has an implied "not to scale" note with it, but I don't think that's a particularly useful argument.
Heck, if you're editing something in MS Office it'll show you an 8.5x11 page with a scale meter. Set it to 100% and surely that's to scale.
Nope, 100% of some other totally arbitrary scale. That's what you wanted, yeah?
But I'm designing when I'm in Word, it's not necessary or convenient to do all of my work at 1:1 scaling, that's what the ruler is for.
Compounding the problem is that the operating system relies on the monitor reporting its physical size correctly via EDID and for a lot of vendors (most notoriously Dell) this isn't guaranteed either.
They already exist (vw and vh are percents of the viewport width and height respectively). Renderers "relativised" supposedly absolute units because 1. they already were not correctly handled (as output devices often don't correctly report their densities and renderers would then just fallback to 72dpi or whatever) and 2. they were ubiquitous.