"In case users prefer native decoding speed over Wasm, F3 plans to offer an option to associate a URL with each Wasm binary, pointing to source code or a precompiled library."
They are not suggesting that the code at the url would be automatically downloaded. It would be up to you to get the code and build it into your application like any other library.
"In case users prefer native decoding speed over Wasm, F3 plans to offer an option to associate a URL with each Wasm binary, pointing to source code or a precompiled library."