I think that this idea does have potential merit, and I don't see it as an instant "disagree". What the op failed to do, however, was flesh out the idea more fully.
PROS:
Outside of Regalia, you can wear armor AND have your skin showing! This seems obvious, but let me explain. Instead of everyone looking like shiny, swirling little purple demon faeries, we can actually alter our skins to show custom armor. Are you a knight of a noble family donning a steel suit of armor? Show it off! Are you a warrior of the OCCVLT? Let them know by showing the pentagram painted in pig's blood across your chest. Moreover, with the changes to how skins will work in 1.8 with the extra "armor" layers, this will only expound on the potential of this.
I feel on this server, we have tremendously talented skin artists and individuals who spend an extraordinary amount of time procuring or creating these skins. I think this proposed change would help a vain creature such as myself help make PvP more interesting by incorporating the RP elements of a medieval skin. There is only so much one can do by renaming multiple sets of enchanted diamond armor and/or dying named leather armor... at the very least an option, perhaps?
CONS:
There is an argument in the mincraft PvP metagame that players rely on seeing another player's armor to better assess decisions made in combat. The most relevant example being: "That guy's helmet is broken! Get him, he's dead meat!!!" With this implementation of such a plug-in, this will obviously be nullified.
However! I do feel this has become so ingrained in minecraft's PvP culture, and I don't know why. I think it is interesting to have a sort of "unknown element" when engaging your enemy. In reality, unless there is a huge size difference, it can be difficult to tell how competent your opponent is in combat unless you have outside knowledge from beforehand. Is my enemy wearing armor made from the scrap, or is his brother a skilled blacksmith that makes crappy looking, yet strong no-nonsense armor? Is she a novice or expert swordswoman? One will have to fight her to find out.
Not only that, but I have noticed some of the "PvP" crowd changing their nick names to the usernames of other players. With all the enchanted diamond armor and weapons everyone has running around, it can be difficult to distinguish, and the use of such deceit seems kind of nonsensical and out of place in a roleplay perspective.
End notes:
There are certainly more arguments for both sides, I just feel that there is more to this than these aforementioned posters have stated. There is definitely potential to this idea if worked upon.