The strange bit with Elm is that it limits its type system just enough that compile times should be reasonable: The performance pits that Scala has are skirted altogether by Elm. If Elm isn't faster at compilation time, it's because that's not where the focus has been. I might be missing something though, and I'd be happy if Evan corrected me on this one.

As far as Scala goes, Grzegorz Kossakowski has done work trying to get major performance improvements out of Scala type checking, and his numbers look very promising. Barring some Shapeless-style type level computations, Scala could compile quite fast.