Aukustus, I'm not really fond of stat requirements on items. Immersion breaker, fo' sho'. I mean, even if I'm a 100 pound shrimp I should be able to pick up a 20 pound greatsword and swing it around. Just like I'm 185 pounds, can only bench 150 but I can pick up a 40 pound dumbell and knock the crap out of you with it. Heh. Can I "knock the crap out of you with it" as easily as someone my weight who can bench 400?
Of course not. But imposing artificial limits like only certain classes can use certain weapons/armor, or you can only use certain weapons/armor when your physical abilities reach a certain level? I don't think it has any business in an RPG, where the very nature of the game is supposed to encourage diversity of action(s).
You know what DOES make sense though? Imposing spell restrictions based on intelligence. Mental abilities (or lack thereof) would realistically restrict acquiring certain knowledge, or levels of knowledge. You're just not intelligent enough to comprehend the required methodology. Well, it makes more sense than restrictions based on physical stats at least. 
I'd recommend going with an open approach. A wizard with 0 points in strength can strap himself into a suit of full plate if he wants, but he's going to move as slow as a snail and/or exhaust himself doing it. Likewise, a warrior with 0 points in intelligence could learn any spell he wants but it's going to take him 10x as long as someone with 10 intelligence and/or way more time/mana to cast. Same with dexterity. Anybody can stick a bolt in a bow/crossbow and pull/wind back the string, but those with high dexterity can reload/shoot faster and/or with more accuracy.
Take care!
Completely agreed with the exception of the fact that people DON'T get snail-slow by using heavy armor, sure it affects movement speed to some degree but what really stands out is how quickly they get tired by wearing it.
It is time to treat armors as they are and not how games want us to believe they should be. I really don't give a damn if mechanics is the excuse - this is just an ancient concept with strong roots in D&D's absurd yet unrealistic mechanics and it should be replaced with something "new" and far more accurate. This is what avoiding the standards should be all about. I don’t mind at all playing a game with traditional and unrealistic armor management but I would definitely prefer having a game applying realistic armor behavior.
"A complete suit of plate armour made from well-tempered steel would weight around 15-25 kg(33-55 pounds).[2] The wearer remained highly agile and could jump, run and otherwise move freely as the weight of the armor was spread evenly throughout the body." - Wikipedia
I've carried around nearly 20kg of weight in my huge backpack for hours. I'm talking about a weight similar to a complete full plate armor set, concentrated just on my shoulders, not evenly distributed throughout my whole body as it would happen if wearing a medieval full plate armor. Nowadays soldiers actually carry way more weight into battle than those in medieval ages. In some cases a modern soldier can carry more than 50kg of gear. Wearing a heavy armor in medieval ages was NOT that hard as people seem to believe nor how games want us to believe, in fact back on medieval times everything people did require more effort making them physically stronger just for carrying out their daily tasks. This implies that people back then were better prepared to wear heavy armors than we are today.
The armor’s major negative side effect is indeed affecting the rate at which you get exhausted plus having closed helmets penalizing your sight’s field of view quite harshly. Any man having no physical disabilities can wear a chainmail or a even a full plate armor while remaining quite agile, assuming we are talking about well-made, full articulated armors. Yeah, wizards would be able to move their arms freely to cast spells, assuming they actually need to perform silly choreographies to cast anything.
Stop treating rogues and wizards as debilitated beings. Let them use a full plate armor as good as a regular person would. Make endurance / stamina the one requirement to properly handle them. The trick to use heavy armors is mainly habituation which will exercise both your endurance and strength. Sure having strength helps out but if one doesn't have endurance to handle it HE WILL run out of breath quite quickly, so endurance should be looked definitely as more important than strength. The fighter is actually the one class that would suffer most from a wearing a heavy armor as it relies more on physical effort, fortunately he does train endurance and strength to counter this.
Another funny thing about armor in games is having chain mail often being classified as light armor while in reality some could actually be heavier than a full plate armor. Full plate armors had in fact their weight way better distributed throughout the user's whole body than the unbalanced weight present in chain mails making chain mails harder to bear. Of course this is quite related to the chain mail ring's thickness and diameter but for any chain mail offering decent protection alone a considerable ring size and thickness was used; light chain mail was mostly used as a complement to plate armors.
Mechanics wise, exchange the wizards carrying capacity for carrying out his heavy armor. Train its endurance and a little bit of strength instead of intelligence or any other wizard related attributes / skills so he can better handle his armor; penalize the character's evade chance based on carrying capacity (armor + inventory); decrease the characters' sneaking ability for wearing heavy and / or noisy armors; penalize mobility speed related to the armor's total weight. Yeah, these are obvious mechanics, however, everything should take both endurance and strength into account but not in a way that would make a particular armor type feel incompatible with a particular class, unless we are talking about extreme armors and character classes - common sense should still be applied.
For the rest of item types, it is pretty much like as Morcrist stated, let attributes and skills restrain their usage and performance instead having character classes "forbidding" item usage types.
PS: Sometimes I spend a full week just collecting information regarding a certain subject. It happens that the armor's topic has been already one of the subjects that I heavily studied before setting it up in my ongoing project.
