WASM code by itself can run at near C speeds, but where you are going to find the challenges is crossing the wasm <-> "rest of our app" divide. You can call fu

WASM code by itself can run at near C speeds, but where you are going to find the challenges is crossing the wasm <-> "rest of our app" divide. You can call functions living in WASM with integer arguments and WASM can call functions you expose to it. You're host app has access to the WASM memory space though, and with those tools you have to craft your API. For a text editor there are going to be quite a few hoops to jump through and memory copying going on just to let a plugin read the document text. Platforms like JVM, .Net, and nodejs/Electron have a huge advantage when doing extensions because they are can easily load code at runtime, and pass "platform native" data structures directly into extension code. Compilers exist for many languages which can target these platforms.