Wrath worlds could become the servers for unusual rulesets. Like the last firestorm server. A wrath server like that with forgotten attacks for example.
Firestorm servers are not that frequent but getting more so. I think the server frequency should not include vet and championship and the like. Those should be special events. That would leave the tiberium and wrath servers, about 6 a year? Maybe more if wrath was to handle more unusual rulesets.