This suggestion may be in the category of wishful thinking, but I think Sorcerer King can take a page out of the other recent very successful asymmetric strategy game: FTL (Faster Than Light). A very nice feature in FTL that I think goes a long way to enhancing the replayability of the game is that whenever you finish the game with a particular spaceship, an alternate design for that spaceship is unlocked.
This goes completely beyond the cosmetic, the new ship design allows you to play the game entirely differently.
What is attractive about such an idea (other than replayability for the user) is that it requires very little in terms of new art assets; and it allows the game designers to explore an alternate interpretation of the "tyrant", "guardian" and "warlord".
Where, for argument's sake, the Wizard (normal) has the ability to use hypnotism to change the allegiance of enemies; the Wizard (unlocked) may instead receive units for free (no cost no upkeep) every few turns through his ongoing summoning rituals.
Where the Guardian (normal) can return broken land to healthy nurture, the Guardian (unlocked) might have the ability to prevent land she controls to become broken in the first place.
This has an additional advantage that (even more) unbalanced abilities can be brought to bear in the alternate form of the sovereigns; they represent a "Game+" form of play and it is okay for things to be (even more) derailed than in the normal game.
