> and they're server-readable too now, just indirectly.

Could you point me to more reading about this? It's the first time I've heard of it

I think they mean that you can always send back the content of a localstorage property with javascript grabbing the value and sending another request back with it in the body. Since the front end is going to run any javascript the server sends it (disregarding adblockers at least), it's sort of a more indirect version of Set-Cookie.