I've been thinking about this. For mobile users I could see a server that collects all the notes from their preferred relays, filters out the duplicates and sends only the unique ones. Right now if you're connected to 10 active relays you're getting 10x the same events. A service like that could also swap out image urls with urls to a compression service that resizes/compresses the images for the client on the fly. Just thinking out loud here.