I'd like to see this added as well, it would help converting dialog to the supposedly better 'map' option.
After some testing (win10 & win7, 100% dpi aka no dpi setting) it seems the ratio is 1.336 for $mapw and 1.228571428571428571428571428571 for $maph (via bigfloat math, 1.228571 is ok for all practical purposes?).
With that you can convert any size and coordinate and get a dialog that looks the same with map than it looked for dbu.
As well as a better/more standard spacing, map is meant to work with dpi settings, when dbu is not.