“Notifying the server” is already done by browsers by just making a regular request. Prefetching links has been a thing for a while now. You don’t need HTTP/2 to do it.
This prefetching implementation is extremely simple fails gracefully. No complex browser APIs used to imitate a normal browsing experience. It all just works as it just goes through the caching system. I'd say this is nothing like existing prefetching implementations, which don't seem to be used much and no wonder.