Do you think Go fulfills that for you today or do you think there's still space for a new language here?
I can readily see a Haskell inspired System F derivative the compiles down to valid Go, or a more flexible, special cases type theory that encompasses all of Go like Ts->Js. Likely a ‘transpiler’, I hate that term, to Go implemented in Go and you have a self-contained language with more advanced type features and Go’s green thread runtime.