If I'm reading this correctly, they are not planning to add a JIT but just the f...

If I'm reading this correctly, they are not planning to add a JIT but just the features required for implementing your own:

    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.

From https://github.com/WebAssembly/design/blob/master/FutureFeat...