[pessimizer]

> DPI is one of my pet peeves, together with points. Why not use mm for font size?

Easy halving, the same reason why A4 has been extolled.

[Symbiote]

Defining 1mpt = 0.1mm would be just as good.

Normal text would be 40mpt = 4mm = 11.33pt.

But there are already metric point definitions: https://en.wikipedia.org/wiki/Point_(typography)