i use the "cache relay" option in nostrudel to a running instance of my relay-in-development and there's no in-browser caching at all, everything is fetched from wherever and pushed to my relay, and fetched from my relay after that, meaning it's instantly available
this is a killer feature that is difficult to do without NIP-42/NIP-46 working for most clients that don't have this inbuilt option
it would enable mobile devices to connect to only one relay and only receive the event once from upstream and then not need it again if the device had its own relay cache