Disclaimer: This is from a purely aesthetics perspective. I know these are not important/do not affect gameplay/would not be noticed in a match, but I sincerely hope it would be considered for future updates if many feel the same.
The AOE series typically had iconic units that show very era-specific looks. For example, the AOE2 knight:
You see a clear progression from a early-high medieval kite shield and chainmail (the helmet in original AOE2 is hard to identify, in DE it is actually a late medieval helmet, which is not so consistent) → typical high medieval greathelms → typical late medieval helmet and plate armour, which kind of matches this:
Similarly the AOE1 swordsman (minimal bronze armour → typical greek helmet → typical early imperial roman helmet), the AOE3 musketeer (cavalier hat → tricorne → shako) had a clear time progression in their designs.
In AOE4 however (correct me if I’m wrong) I don’t see a lot of such progression, especially for the most iconic units: the knight of course. All units seem to start at high or late medieval. Even the “early knights” that the French also started with a very late-medieval looking in feudal age (similar to the 1400 one), and I was expecting something like a typical norman knight (the 1100 one). So instead of having a “early-high medieval knight → high medieval knight → late medieval knight” progression, I feel more like getting a “poorly-equipped late medieval knight → better-equipped late medieval knight → golden saint late medieval knight”. Same with the early MAA. I was expecting round shields or kite shields, but ended up getting a poorly-equipped late medieval guy with a heater shield.
The only game with a similar design approach afaik is AOM (maybe AOEO as well?), but AOM is half-fictional and already has a very distorted timeline (hellenistic greeks vs bronze age egyptians vs early medieval vikings), so each civ is kind of “trapped” in their iconic looks. AOE3 native americans used a similar approach, because their scope is also very limited. But AOE4 is more historical, and all the civs had long and continuous history, so I believe it would be a better idea to add a few more distinctive designs that reflect the progression of ages.
However, I would also like to point out that (1) such “progressions” are more of stereotypes rather than actual history (2) the actual scope of the unit and weaponry design in every AOE is much narrower than the timeframe it proclaims (for example, AOE1 chariots and cavalry appear at the same stage, AOE3 musketeers start with bayonets despite having the most iconic pike-and-shot look). So every AOE feels more like “building up a backward base in classical antiquity/high medieval/18th century then upgrade it” than “really progressing through early-middle-high ancient/medieval/modern eras”. But more flavor would be welcomed.
This is just an impractical proposal. I don’t know what people think about it.