I heard this directly from a higher up at MS during a conference afterparty. He said he couldn't wait for browser support for Web Assembly to go live so he can show the things they're working on.

And yeah, for C# to WASM, we'd need garbage collection support in WASM. That doesn't exist yet, though it's on the list of future enhancements[0].

[0]: https://hacks.mozilla.org/2017/02/where-is-webassembly-now-a...