Yeah, believe me, I understand the reasons for self-hosting in something like Rust versus not self-hosting in Julia. Also the fact that Julia is almost all Julia.
Still, the fact that it's almost all Julia suggests to me it could be all Julia, although maybe that's changed with 1.0+ releases.
Trying to think about why it matters to me, I think what it is a sense that if you can get what Julia offers from another language that does more, it probably is better to use that other language. So I want to see it pushed to be more general-use. Not just for the principle, but because I think in general there are gains to languages in doing so. E.g., my guess is that getting Julia to be self-hosting would require certain efforts that might pay off in other ways, or set the stage for such things.
I think that is worth it for Rust because I think it has good features for building compilers. And really low level runtime-y bits.
Julia has less good features for building compilers.
But still the vast majority of the language is in Julia. Including a lot of the code lowering.