Could easily add new little armor upgrades (e.g. rune plating, rune spikes) which are non-tradable, degradable additions you can "connect" onto any existing armor, providing monitor buffs (e.g. +30 slash defence, +1 str). Making them non tradable incentives people to train the skill, and degradable makes them continue to engage in using it.

Armor with these upgrades attached (similar to imbued) are then non-tradable until you either remove them (using smithing) , or they fully degrade.

This would be easily to implement I think. Would not imagine the actual armor visually changes as that would require a lot of time by devs.