I tend to think that this is the one thing that would bring a v2.0. Compile time, startup time, binary building, and native code caching improvements I think ta

I tend to think that this is the one thing that would bring a v2.0. Compile time, startup time, binary building, and native code caching improvements I think take the big priority here (and I describe elsewhere in this thread how those are really all one technical issue), but when that's completed I do think formalizing a traits interface will be the next major semantic change to the language. It could be a v1.x if it does not require a breaking change to the language's semantics, but it's hard (for me at least) to see how to nicely incorporate trait definitions and required dispatches without making a single breaking change.