This may be real or not, the only thing I know is: armor evolution is not a thing but there's armor forms. There are two main types of armors, I do not know if the pokemon that can access it can have both or if is a exclusive one for each pokemon capable of having armor. Armors basically reduce one stat to boost other. The two types are shield series and sword series, the shield series incresses defences and the sword series increases attack. Some pokemon have armors that increase both special and physical, others just one. Each pokemon will have exclusive armor items like the megastones. Apparently some fast pokenon with low defenses will have armor that will reduce speed to boost defence. The idea ia to add more variations to the way a pokemon can be used. The armors will work as forms and the pokemon will remain in that form as long as he keeps the item. The total base stats of the pokemon won't be affected if it gets extra 50 base defence those 50 will be substracted from other stat. Most armors that boost defence usually reduce speed.
That's what an insider told me.