My only complaint here is that they're not replacing it with some generic way for the server to specify a client-side (WebAssembly?) program to transform an arbitrary response body into HTML, like you could do until now with XML and XSLT.
That'd be a hell of a lot cleaner and more elegant than sending a mostly-blank HTML page with a script that separately fetches and transforms the actual content.
And it would be easier on the server than server-side rendering.