No, I don't think it will. Pointers to managed objects are opaque, and aren't actually backed by the wasm memory buffer. The managed heap is offloaded.

Shrinking the memory object shouldn't require any special support from GC, just an appropriate API hook. It would, as always, be up to the application code running inside the module to ensure that if a shrink is done, that the program doesn't refer to memory addresses past the new endpoint.

If this hasn't been implemented yet, it's not because it's been waiting on GC, but more that it's not been prioritized.

Wasm GC is entirely separate from Wasm Memory objects, so no, this does not help linear memory applications.