Well, medium armor provides a nice range of gear that NPCs/ “monsters” can be outfitted in to reflect their background, financial resources, etc.
PCs, by contrast, always have one of, what, about 5 numbers as their AC? Pretty dull, but players generally seem to pick their armor by the numbers, not for any background or setting related reason. It is very nice, I think, to have the other types available to make the setting more diverse.
I don’t think the “none, leather or plate and shield” (to simplify a bit) situation with PCs will change.