On a server I play on, I have an "Instant Kit Machine". Basically, its 10 double chests with various items and when you press a button it gives you iron armor and a sword. Whenever I get new armor, I always sort it in the correct chests. This is very time consuming and boring... so I looked into item sorters. These would work but theres a problem--- armor isnt stackable so you cant do a threshold. Is there an compact hopper sorter design that would work to these requirements?
But you could just make four hoppers leading to separate armor chests and throw each piece of armor in the correct hopper. It's not that hard. And remember, just a few months ago there were no item sorting systems outside of mods that could store them after sorting, so don't take sorters for granted.
A few weeks ago I know there was a youtuber (I forget who) working on this problem. However, their method still required non-automatic sorting. Basically, they were building a very elaborate shipping system that could track the armor through the system, but you still had to tell the machine what each un-stackable item was, first. I doubt that a solution to this exact problem will ever show up in Vanilla. It just seems to be a limitation that the game makers are happy with having. Sorry dude.
Let us know if you come up with a useful solution though! remember, you don't need the solution you want, you need a solution that works. Good luck!