Rust can link 32-bit code that can run 16-bit segmented mode [0] and if you can figure out the right set of protected mode magick, you could almost certainly get it working in flat mode.

I started working on a DOS-based project and played around with Rust before deciding that it was going to be tough and would not be as optimal as just dropping to C and using OpenWatcom which is pretty capable considering its age, IMO.

[0] https://github.com/o8vm/rust_dos