I have hope WebAssembly can make it happen. If you compile Qt and target WebAssembly, and compile Rust and target WebAssembly, it should all be able to work together automatically without needing tools like SWIG.
You can already compile Rust to x86 and Qt to x86, yet they don't work together automatically. Is there any reason to expect WebAssembly will be different?
I'm unfamiliar with WebAssembly, but I thought the spec was a little higher level. Two x86 apps might have the same op codes, but they don't always have the same calling conventions. How do you call a C function? You can't tell looking at the binary output, you only get the symbol name. Is it cdecl, stdcall, how many parameters and the names and types? Kotlin and Java work together, so do C# and F#.
ABI would still be a complication here, as different languages have different ways of calling into each other, different name mangling rules, etc.