We'll start tackling GC as soon as we finish the MVP [0]. No timeline yet, but we consider it essential to the high level goal of integrating well into the existing platform.
[0]: https://github.com/WebAssembly/design/blob/master/GC.md
[0]: https://github.com/WebAssembly/design/blob/master/GC.md
[0]: https://github.com/WebAssembly/design/blob/master/FAQ.md#is-...