I like the idea, however based on a skill type world I wanna say something like skill level on weapon be the requirement to equip it. However I can see something like this working for armor like proficiency.
I'm going to disagree with artificial barriers being a fun aspect, mainly due to the fact that not everyone is going to build their character the same. Single player RPG's it may be fine, however with the amount of flexibility SE has said they want us to have, why pigeonhole us into needing X stat instead of playing around with our stats to see what works best.
And this is why. Being able to further customize our characters growth and setting certain requirements for certain pieces of gear can not only give the player an idea of where to balance stats at, but also adds more to customization (I hate seeing everyone wearing the exact same EG gear).
Also the ability to change armor during battle is unrealistic and would like to see a more real vibe to this. And not being able to change weapons in battle is the opposite since in reality it would be easier to change weapons than body armor, and making both unchangeable during battle makes it this way.
Not saying it would be this way, but stats effecting not only if high enough to equip said armor but type also. And I'd rather see weapon requirements based on skill level over class level, but that wouldn't matter too much. The above system I don't see working saying you lvl one class to cap and get uber weapon for class you never played before. Makes sense to me to get proficient with the weapon type before you can equip one of such great power. Just my thoughts on the matter.
Asyrian - 90 Drg/Mnk
Reisaki - 90 Blu/Dnc/Pup/Rdm
Majoga - 90 Pld/Nin
Belisi - 90 Sch/Cor/Whm