In my opinion that should be either pure javascript or better, typescript. Lots of people know it, tremendous amount of tools, IDE's, testing frameworks, etc. Also integrating ability to use frameworks like Angular with ts can finally make dapps useful and beautiful and not that ugly looking geeky ones we have today. Bridging gap of dapps and users...
I don't know enough about Typescript and it's improvements, but for javascript at least, I wouldn't want to trust millions of dollars to some code written in Javascript. Similar to Solidity there are just too many pitfalls and ways to write code that looks clear and concise but has unexpected behavior. If you want a laugh, watch this "wat" lightning talk (it covers Javascript 1 minute in) to see what I mean
https://www.destroyallsoftware.com/talks/wat