WebAssembly as a platform for abstraction

[Joseph Rushton Wakeling]

Came across this interesting article recently about how WASM can 
be used to make it easy for users to add their own application 
logic:
http://adventures.michaelfbryan.com/posts/wasm-as-a-platform-for-abstraction/

... and hard not to think in this context of John Colvin's 
prescient remarks about the importance of WebAssembly from way 
back in 2015:
https://forum.dlang.org/post/tnzujgocuuvmkdqdsjmm@forum.dlang.org

It's arguably a bit late by now to be "catching a wave", but 
what's the current state of the art in D's WebAsssembly support?  
And does anyone have any experience of using it as a way to offer 
extensibility to end users?