It's currently possible to equip weapons while lacking the proficiency for them, at the cost of a hefty AB penalty. This is a small mechanic that I greatly appreciate.
I am wondering if a similar system could be implemented for armor, where one can equip any armor but their AC will be prohibitively reduced if they lack the proficiency.
For instance my commoner is a smith and one thing I enjoy doing is creating personalized equipment with individualized appearances and descriptions. Currently I cannot fully do this for heavy or medium armor due to being unable to equip it.
There are other situations where this might be relevant like disguises, costumes for plays or parades.
I'm not sure if there's some kind of room for abuse here that isn't immediately obvious to me, or if it would be prohibitively difficult or awkward to add for backend reasons, but otherwise it is a feature that would be appreciated by some.