The tldr; is Will wants to write a fast Nostr client that runs in a browser.

nostr:npub1xtscya34g58tk0z605fvr788k263gsu6cy9x0mhnm87echrgufzsevkk5s wants to write an app in Rust (which often surpasses C++ in speed but without as many ways to shoot yourself in the foot) to WASM instead of native machine code for a certain CPU. WASM can be executed by web browsers at speeds that are starting to approach native speeds and are certainly much faster than JavaScript.