What game you play have direct copy when switch server?
Almost any online game? Even Runescape 15 years ago allowed you to change servers when one was full. Still does. It's incredibly common in MMO games as well as any other game where you play online. I mean look at Destiny, you're constantly switched to new servers with different users browsing the game world.
The issue is that it seems like much of the character data for this game is tied directly to the server, rather than to a separate player account database. If that were true, it would just be a matter of loading X account into whichever server was least full. I'd imagine if they built it the first way, changing that now and having a dedicated account separate from the servers would be a massive challenge.