The design documents clearly state that WASM is intended to be a compilation target for C-like languages, and in the future may also contain a GC and an optimizing JIT.
Languages requiring a GC and/or not amenable to AOT optimization should -- at least for the time being -- continue to target JS as a compilation target (or implement their own runtime in a C-like language and embed it in WASM).
WebAssembly should support:
Producing a dynamic library and loading it into the current WebAssembly module.
Define lighter-weight mechanisms, such as the ability to add a function to an existing module.
Support explicitly patchable constructs within functions to allow for very fine-grained JIT-compilation. This includes:
Code patching for polymorphic inline caching;
Call patching to chain JIT-compiled functions together;
Temporary halt-insertion within functions, to trap if a function start executing while a JIT-compiler's runtime is performing operations dangerous to that function.
Provide JITs access to profile feedback for their JIT-compiled code.
Code unloading capabilities, especially in the context of code garbage collection and defragmentation.