Well, there're obviously a lot of things you could improve to lower the chances of a DDoS. (E.g. introducing a TTL / maximum number of hops for a message or forwarding some messages only to some peers, thereby influencing the exact way messages are routed through the network.) But I agree it doesn't look like the most viable idea for a medium for mass communication, not even if it's just for high-latency messages. Yet, people are working on it.