[nebopolis]

I would argue that Fortran _is_ "über mainstream" - if you look at computing as a whole. It may not be used extensively for CRUD applications, but it is part of the bedrock of basically all computing. And there are some niches where it is the main/only language.

Rust will likely end up in a similar place - enormously useful in its niche, foundational for infrastructure outside, and with enough uptake and stability to make a career out of. I don't think anyone expects it to eclipse popular dynamic languages for web development, but it might make inroads on C and C++ in areas where active development is still needed.