I think he's suggesting that one of his criteria for package selection is his ability to contribute changes to the upstream project if needed, which he feels he can't do for TypeScript on account of him not knowing the language.
I know it is annoying that there is a breach into the purity of the JavaScript language by a different actor. But let us face it: TS is useful, it is the right tool for the job and it is not niche. It complements JavaScript and solves problems JavaScript is structurally unable to solve. It helps and improves the JavaScript language. It helps millions of developers with static typing backgrounds to accept and deal with the imperfections of JavaScript.
In my primary language - C# - there is tons of influx of functional programming nowadays (sourced via F# and OCaml). I could fight against it but I do not. I embrace change and adapt. Take the Linux Kernel: After three decades of C code they are talking/merging support for Rust. Why: it is the right thing and it is a good complement for their C tooling.
You're probably right. My argument, however, was purely about separation of concerns: different language means different package manager (or namespace...).
We're going to start seeing a lot more WASM stuff on npm, which is going to be whatever language anyone wants.
The VM for typescript is node/browser. Because it gets compiled to target those.