Just what derok said.
It is possible to make them, one mod already has sort-of tail armor. (Argonian mercenary armor?)
So yes, fully doable.
Maybe a bit simplier approach would be to make it separate piece of armor, so you don't have to tinker with every armor to link it to tail mesh containing the armor (And most likely breaking many mods at the same time)
Yeah. It would have to be ~34 models altogether (if you included all armour types) which would be 17 in-game items.