None of these changes impact HTTP server code. Pages that run javascript might want to set some new headers, but setting headers is something that web servers always have to do. Changing a site config to send some new headers is work for a web page creator, not the HTTP server developer. And the changes are backwards compatible, so you don't actually need to do anything if you don't want to.

This new complexity is about javascript execution, and creating a browser that can run javascript has never been simple!