I've always been bemused by the major focus that we need a brand new implementation of the algorithms so that they can take advantage of modern computers. Ignoring just how bloody well it already takes advantage of faster processing power.

(I get that there are some good arguments for a more developer friendly extension language.)

I think Latexbase does something like this (they claim it works offline too, using service workers). They claim to be using Emscripten/LLVM but it doesn't seem like they use wasm yet (probably because they didn't consider it a viable option back in 2016 https://latexbase.com/p/b0a174a5-09b3-4598-9686-3a73be2dc8e5). And while it's not open source I still think it's a really cool proof of concept..