There's some ongoing work on a LLVM whole-program backend for the MOS 6502, which can already compile some Rust code (discussed https://news.ycombinator.com/item?id=28581812 ). If that's successful (it does require lots of new optimization passes to match the effectiveness of hand-written code), it would be quite easy to have a backend for the Z80 as well.
A Z80 backend could probably reuse our static stack allocation, but that's about it. It's definitely useful, but the time-consuming part of writing LLVM-MOS's code generator has ended up being... writing LLVM-MOS's code generator. The static stack stuff is maybe like 250 lines of code, and I haven't had to touch it in months.
