D&D 5E Wizards Banned from Armor (Your Fluff Wanted)

[Mistwell]

Easy, simply give casting proficiency in armor to specific classes instead of a global rule, and /thread

I think you missed his point. In that he is not looking for a way to mechanically accomplish this (mechanically accomplishing it is the easy part - you just declare they cannot do it). The clue is right there in his first sentence, where he cleverly hides the fact he's looking for a flavor thing instead of a mechanical thing by saying, "So, this is totally a flavor related question...".