There was an interview a while back ago where Adam Isgreen talked about the future of AOE 4 and most importantly he talked about Red Alert and how he wanted to bring similar technology tree/unit choices as seen in the RA franchise.
but in Red Alert 2 they made it more interesting by introducing different harvesting trucks to different factions (teleporting Allies, armored Soviet).
Based on that it seems unlikely that the civilizations would showcase as extreme differences as StarCraft does. But It does seem like the units would be more diverse than what they are in AOE 2.
IE small tweaks to units damage, health, upgrade path, etc based on the civilization type. Main thing being that all civilizations would have Archer, Cavalry, Swordsman and Siege unit line which all would work similarly enough to make playing against them simple enough so that no one would have to learn every match up in order to play the game competitively.