Adding a .NET backend to Rust could give you high-level two way interop.
Adding a similar backend to LLVM would let you use .NET target similarly to WASM in that you could compile pretty much any software (C/C++, Go, Rust, etc) and run it on any supported platform without recompiling (well, it would JIT). But you'd have to stick to C-level APIs.
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I think these two have different use cases.
Adding a .NET backend to Rust could give you high-level two way interop.
Adding a similar backend to LLVM would let you use .NET target similarly to WASM in that you could compile pretty much any software (C/C++, Go, Rust, etc) and run it on any supported platform without recompiling (well, it would JIT). But you'd have to stick to C-level APIs.