I would prefer it just gets baked in to Demonic Tyrant rather then having another ability to manage. I'd hate to see different tyrants locked behind talent choices but it could be cool to have a different model based on a talent you pick. Obelisk, Pit Lord, Void creature, Imp Mother, and more could easily be viable additions.
I could also see a passive that summons a obelisk interesting as well. Dogs or Imps could proc it and offer a small buff.