... if relays start connecting to each other. One simple improvement would be sending "I have a message with this hash, do you want it" messages, and only sending the whole message upon request. That's how the bitcoin network does it with inv & getdata messages.
Discussion
That would be useful even with the current topology where clients connect to multiple relays and could receive the same message, in full, up to 10 times or so.
Commercial relays will probably want to connect to other relays in order to serve their customers with more content.
or it can download every event from every relay and feed the relays that lack an event, directly without asking.