Guest monsters in higher difficulties

The most of us who played Diablo II - Lord of Destruction clearly remember, that this was one of the best ideas for Nightmare & Hell diff. in order not to be bored so easily.

Guest monster means, that there are monster types mixed between acts.
Would it be possible here actually? It would add to the atmosphere, not to mention that it could give the game more variety.

Actually, guest monsters only appeared in act V on nightmare and hell difficulty.

I thought we already did - they’re called Nemesis heroes. :smiley:

Two of the superbosses only appear in Ultimate. There’s an unique boss in Ancient Grove that only appears in Ultimate.