Well, I could see different level of effort for such thing, from a sample color swap and variable stat change, to more something more fancy.
Still, a unique, named enemy that are challenge to defeat would certainly add a sense of extra achievement (not to mention the special rewards)
Hopefuly, they might even open this part up for moding, so crowd source the effort.
Other boss could be like a D’thor the Fellmancer (fancy necromancer), Sander the Fox (fancy Bandit leader), ,Zorko the Butcher (fancy Orc zerker), etc. You get the point.
