> Instead, the replace directive needs to be at the main module, where it doesn't make sense and is inconvenient.

Wait, what? If you decide, in your own application, to force all your dependencies to use a specific version of golang.org/x/net/http2, then obviously you'd want to be able to put this directive into your own application's source instead of going around patching 3rd-party repositories (that's just rude).