I think 3 servers is the perfect amount, we shouldn't need a 4th. Like, you can only go so far until it's just a stupid amount.
For example, 2 arms is perfect, having 8 arms would just be messy for a person.
But octopi do just fine!
But for realsies, merging all the servers would be a laugh and a half. Warning would defs be needed though, so users could change emails in order to keep all the accounts; or they could have an account switching system so one is able to have multiple accounts associated to one email. Though, that could allow for a team of clones.. Would definitely be interesting, but would make for a very unlively team.