Wasm now supports multiple modules and multiple linear memories per module, so it ought to be quite possible to compile C to Wasm in a way that enforces C's object access rules, much like CHERI if perhaps not Fil-C itself.
Some WebAssembly runtimes now do support those parts of the specification.
You wouldn't be able to get quite as fine-grained. One memory per object is probably horrifically slow. And I don't know about Fil-C, but CHERI at least allows capabilities (pointers with bounds) to overlap and subset each other. I.e. you could allocate an arena and get a capability for that, and then allocate an object inside that arena and get a smaller capability for that, and then get a pointer to a field in that object and get capability just for that field.
The multiple linear memory is supported in wasi preview 3? I thought it was not supported as of preview 2.