One of the things that I think make this tricky is that if you have any DOM references you now have visibility into a GCable object.

Part of the web Javascript security model is that you cannot see into garbage collection. So if you have some WASM-y pointer to a DOM element, how do you handle that?

I think with GC in properly people might come at this problem again, but pre-GC WASM this sounds pretty intractable