A realistic way to add dragons.
Considering this is a pve game with no pvp, what about building more onto that fact?
Once a month, one player can become a dragon, which lasts one year. So there would only ever be twelve dragons. Wouldnt matter if they are overpowered, since 99.9% of people won't be a dragon.
The means of how this event comes about is up to you. Would be VERY COOL to see a player dragon once in a blue moon.
I know that a casual like me would never become one, but just knowing there is a rare almost unattainable class out there adds something magical.. well at least to me.
I am also sure that it will keep people coming back at least once a month to try to be the lucky bastard who gets to be a dragon. Hopefully it's overpowered and awe inspiring, or it will miss the point of this entirely haha.