When kayle gets her rework

I really doubt this would happen. Kayle being fully armored is one of her main appeals and is even a plot point in her lore(sure the lore will get retconned,but there are often aspects that carry over),as she isolates herself from the outside world with said armor.

Why should unmasked Kayle be her main skin?

That would make sense actually, considering a lot of the newer skins are unmasked now.