No, unless you're designing a protocol to replace IMAP and you want all the proverbial web scale systems to adopt your new protocol. And then again, interoperability and universal adoption is probably something the smaller Dovecot installations would want.
Master-master conflict-free eventual consistency systems are easier and safer to operate, there's no nightmare damage from split-brain and things just work, even in the worst scenario. Master-slave failover is notoriously prone to error, even for small deployments.