Cloudflare already has a heavy dependence on the origin server being up, particularly for non-cacheable dynamic websites, so adding a key server doesn't really

Cloudflare already has a heavy dependence on the origin server being up, particularly for non-cacheable dynamic websites, so adding a key server doesn't really change anything. It has always been critical that you keep the address of your origin server, and now your key server, secret so that it's not targeted directly by DDoS attackers.