It’s just mentioned as an aside in this article, but the work the Mono team is doing on WebAssembly is super exciting. Can’t wait to start messing with it.
This blog post has a few more details and examples of the WebAssembly work: http://www.mono-project.com/news/2017/08/09/hello-webassembl...
Disclaimer: I'm working on Mono for Microsoft/Xamarin (primarily class libraries and tools).