It looks like garbage collection is at the 'proposal' stage, one step before it would start to be implemented.

"During this phase:

    "One or more implementations proceed on prototyping the feature to the point that a comprehensive set of tests can be added.

    "A test suite is added. These tests need not pass the reference interpreter at this point, but should pass on some implementation."

https://github.com/WebAssembly/proposals

https://github.com/WebAssembly/meetings/blob/main/process/ph...

Here's the proposal:

https://github.com/WebAssembly/gc

And you can see it's being actively worked on:

https://github.com/WebAssembly/gc/commits/main