Like the Ziggurats of Warcraft III?
For AoE IV I see it as impossible, especially because in fact, many historical aspects are being asked to be represented well, and it is what is most attractive part of the game is the “Historical” background and “Historical” representation.
Maybe for Age of Mythology, probably for Retold, if it starts to have new expansions, and only if somebody make a model of that system works for a civilization of the past that would have magicians as defensive forces. Babylonians maybe?
Well, there are already magicians in AoM (Age of Mythology): in theory the civ with the most magicians for AoM would be the Egyptians, their priests shoot lightning with little effect on the living, but plenty of power against mythical units, they can summon obelisks and the pharaoh with the power of Osiris is capable of becoming a bird-man hybrid capable of launching lightning bolts from his staff.
Of course, even if there is magic in AoM, it has to have its limitations. The Egyptians were known to have court magicians, priests could do magic tricks, and stuff. For other civs, it would not work the same, since the conceptions of magic, heroes and creatures vary around the religion and beliefs of the civilizations in the game.
If AoE IV was your first game in the franchise, I also recommend checking out Age of Mythology to see how mythology applies to the RTS. There are mythical units, heroes, magic, magic powers of the gods, etc
Other mage-focused RTSs include Spellforce, I, II, and III.
My opinnion about Spellforce Franchise
Personally, I consider Spellforce I to be the best, because you have a hero with a humongous catalogue of spells in disposition and many ways to improve him/her. Spellforce II had an ugly artistic design in my opinion, but its plot was still fun and a fairer RTS system. Spellforce III is a prequel and was made by another company that is not respecting much or at all the chronological line of the 1st and 2nd game, but i had to admit that its first campaign has a good story, design and charismatic characters… but its sequel campaign become as G.I.Joe II, including “progre” things and “multiverse” things that I honestly don’t like very much. For me Spellforce franchise finished with Spelfforce II campaigns, Spelforce III is a fandom prequel.