The new units you uploaded are great. Thanks for the unmasked knight, too. I never was much of a stargate fan.
As for the discussion of Musketman, Grenadier, and Rifleman... I echo Bakuel's commentary about pants v. tunics. In Rome, at least, they considered it a really big deal that the Parthians wore pants and not tunics. Also, I believe that the cisalpine gauls were sometimes referred to as the gallia togata because they wore togas like proper phil-hellenes, not pants like those transalpine gauls on the far side of the mountains.
The fact of the matter is that its very difficult to imagine what egyptian culture, if active and alive, would be like had the Egyptians not been first conquered by the Persians and subsequently by the Macedonians. It's even more difficult to imagine them without Christian, Arab, and Muslim influences (because, at least the Macedonian Ptolemies tried to assimilate and become Egyptian instead of making the Egyptians into hellenes).
Likewise, I think Bakuel is right to try and identify those aspects of Egyptian culture that are most distinctly Egyptian and superimpose those ontop of more modern cultural traditions.
The Arabs, in game, retain much of the Beduin style of dress throughout the game. The Persians, are distincly un-persian for most of the game, and quickly become Arab-Iranians. Contrarily, the Carthagenians retain their Hellenistic-Mediterranean feel and never resort to the Morroccan-Berber-Tunisian-Arabic influences we see in North Africa today. Likewise, the Carthagenians, in game, feel more Greek than Punic.
Compare this with the Americans. If we follow the Egyptian example, at least as they are represented in game, the Americans in the Ancient, Classical, and Medieval eras should be, as far as unit art, similar to Native American Tribes and then transform into European style units during the Renaissance. Obviously, this is not the case. Flavor unit creators have, instead, decided to make American flavor units akin to European and English units until the Industrial Age. The flavor units track the people, not the location.
The opposite is true of the Persians and Egyptians. There, flavor unit creators tend to track the locations and not the people. Thus, medieval and renaissance Egyptians and Persians look more Arab than Egyptian or Persian.
The medieval period saw an expansion of armored soldiers. The weapons and style of fighting saw a progression of military advances and led to more heavily protected soldiers (the traditional armored knight is a good example). However, with the development of gunpowder, quite obviously, this armor became obsolete.
The big question, then, is this: after the use of heavy armor faded away, would early-modern Egyptians and Persians resort to their earlier style of dress, or adopt new ones?
I think the answer will and would come from the social and environmental utility of the clothing. Arab clothing is long and flowing to shield from the heat and the sun. But such a style of clothing is based on hundreds of years of nomadic shepherding where individuals were exposed to the elements and burning sun.
What would the Nile style of living be like? It was always more urban than the surrounding civilizations. What impact would that have, if any? The elements would be less of a problem. Instead, disease (like malaria) and the heat would be the major hinderance.
In the end, perhaps your imagination is as good as mine.