I'm afraid I can't answer your question. Either scenario -- a unified system or a "halfway house" -- might be the case; it depends on the intentions of people w

I'm afraid I can't answer your question. Either scenario -- a unified system or a "halfway house" -- might be the case; it depends on the intentions of people who design programming languages and the number of pretty arbitrary factors determining their success. But since the general trend is that the PL community is heading towards more advanced type features, maybe someday we should see such a language. By the way, I don't think it's time to claim that Rust is a "good enough" house -- simply too little time passed since it was embraced by the community. The language didn't even include `async`/`.await` some four years ago. Macros 2.0 are being developed; a new trait solver too. If after some ten or twenty years we'll find it being a mess of legacy, maybe it is not the right way to design a language.