What prevents a relay to connect as a client to other relays and forward events it sees? This is probably already happening.
Discussion
Nothing prevents it but I think most relays and relay implementations right now don’t do it, but new implementation forwarding relays do exist like
wss://relay.nostrgraph.net
wss://nostr.relayer.se
At the moment clients also broadcast to other relays in the relay list.
Also I saw this from last month https://github.com/phyro/fo-relay