Shouldn't we just switch to dimensional measurements like millimeters, inches, etc and expect the operating system to use whatever metric it chooses to make it display size appropriate (pt, px, em, etc)?

I think the problem with this is that developers (me included) have enjoyed using resolution to to change the physical size components in order to gain screen real estate. Perhaps, shifting to a zoom/scale setting would be a better approach than tying ourselves to resolution.

Humorously, it would be kinda like a print guy measuring font size in fibers and the size of the type changing based on fiber density. :-P Then again, they probably do that.