The concept of physically wearing one suit of armour over another suit of armour is bizarre. Barring that the person wouldn't be able to walk or move, it completely defeats the design concept behind the different armour types. If a player ever made such a suggestion I would respond with a curt, "No".
Nice going. Emotional appeal.
I'm sure the logical gamers you know, if any, will love that.
Anyway, I'd go for a concept of 'ranked armor' wherein one can put on as much plated metal, padding, furs, and chain as desired, but penalties to move speed, physical skills, Concentration penalty with disruption to spellcast (like Arcane Spell Failure but could be overridden), and attack rolls would increase by a proportionate amount. You can literally wear as much as you want (limited by size) but without enough training a PC would end up immobile and with horrible aim.
I tried to stat out a concept for this, complete with rule(s) for removing "destroyed ranks of armor", but the result was criticized as too complex.
For proficiencies, the characters could grab feats to reduce armor penalties that increase in effectiveness by BAB, repeating armor feats then stacking the amount of penalty reduced.
Strength was also vital in reducing penalty; more STR, more armor worn.
Alas, I favor a "BP style" modular armor concept I saw here, in BG, a while ago. I think Zerosum made it.
It used Light, Medium, and Heavy armor categories, which worked much simpler than armor ranks. Less math.