I think both can coexist. WebSockets, common comet long poll, and even the "internal" AJAX APIs of web applications are one thing, addressable URIs to resources

I think both can coexist. WebSockets, common comet long poll, and even the "internal" AJAX APIs of web applications are one thing, addressable URIs to resources another. E.g. Gmail has history navigation and bookmarkable URIs for emails, but no such thing for chat or other page state, which is totally fine. REST with its addressable resources has clear advantages over RPC style apps for many applications, it won't go away. Bookmarks, navigation, the overall simplicity.