I've been wondering this myself, so thanks for the link. Looks like it lives under the label: "Proposals we might consider in the future".
I've been building a [super early/experimental] rust frontend framework (https://github.com/anowell/quasar), and going through Javascript to manipulate the DOM is the cause of plenty of frustrations and limitations, so I'll be keeping an eye on this.
I understand that's on the roadmap, but not high priority.
Edit: No help with a prediction on when, but a bit of the "how": https://github.com/WebAssembly/design/blob/master/GC.md