Rust barely even trying on the pluggable allocators (seems like it's never going to land, afaik "allocator-api" has been sitting proposed in nightly only since 2018) is one of the things that frustrates me (fulltime Rust eng) about the language and makes me feel like it's just a language that's been eaten by web services developers, applications level work, and/or tokio, and isn't "serious" as a systems PL really despite the verbiage.

Building a database, operating system, etc. absolutely requires fine tuned control over allocation. You can get around some of these things in Rust, but it will fight you. You'll effectively have to turn your back on the containers in std and build your own vectors, maybe even your own Box, etc.

Odin looks really appealing to me at one level, but I'd have a hard time switching to any language at this point that doesn't have a borrow checker story.