I'm aware of it. But my previous suggestions were in part shaped by the stated goals of Go's designers: to keep the language simple and easy to learn for non-language geeks. 1ML is really cool, but its type system can be intimidating: small vs. large types, incomplete inference, type-checking as elaboration into System F-omega, etc. OTOH, plain Damas-Milner is dead simple.
Another problem with 1ML is that it's only a research prototype for now, so we can't take it "for a spin". Given the 1ML inventor's main job, this is unlikely to change any time soon, unless some kind soul takes on the 1ML project lead.