I’m actually the person who added the m68k target to the Rust compiler and was also one of the driving forces of getting the backend into LLVM.
Generally speaking, getting a new backend into the Rust compiler is not trivial as it depends on LLVM support at the moment which is why asking someone to just do it is a bit arrogant.
Luckily, both rustc_codegen_gcc and gccrs are being worked on, so this problem will be resolved in the future.