Weapon Condition

very good idea

Ya, day z is different from stalker, and the developers need to ask themselves which style they are going for? do they want such issues as weapon and equipment degrading, or do they want a game that is more day z. Each game concept attracts a certain player. I see the people who are interested in weapon and equipment maintenance etc are the people who are liking the potential of nextday precisely for the reasons that drive people away from day z. the kind of people who want a game to just shoot random people in the face, they play day z. Hopefully next day will bring in more emphasis on a living world, and encourage less of bad behaviour from people just looking for cheap thrills. factors like not using your gun unless you need to, and valuing its continuance, would lend itself to this mentality.
These are my opinions on it anyway. I found Survivarium to be quite a let-down, because although they had a great atmosphere, it just became another pvp shooter, rewarding players who were quick and vicious, but offered no context to your actions. and I think they are suffering for it. They alienated a vast amount of people who are after the stalker feel, and lets be honest, there are enough pvp games out there. the devs here need to find out what makes them unique, and capitalise on that. But of course, these forums will be great for them to learn what is most appreciated in their player list. Personally, I am very interested in equipment degrading through use, and in food spoiling in storage. anything that makes the world more vivid and real, instead of just a backdrop for shooting other players.

the main problem of durability is the rate of its decrease especially if you want some level of realism, a real gun is not a piece of crap after hundred shots, on STALKER it was way to high and after 2 clips your gun was more or less good for being ditched.
For example a barrel is good for several THOUSANDS shot fired, the H&K 416 it's about 10 to 15K, AK-74 is the same life span and this is the "expandable part". If you have to do an overall condition, even on a quite worn gun, that should be around 5,000 rounds fired which is FAR MORE than you shot on STALKER.

And if you want weapon condition, you have to be agree with armor condition and THAT will be another story because counter to weapon, armor are prone to be messed up by weapons and your lovely brown shirt with balistic gear will be thorn to pieces by a single AKM burst. No more 45% all the time, if you loot a 20% on your victim that will be great.

Ok, to get right down to it, there is realism and there is realism.
Guns: Some guns will run quite well with a high amount of abuse. some start fowling up pretty quickly, especially if dirty/substandard ammo is used.
Instead of having a "gun health" like stalker, you perhaps should be able to do a field strip and clean, if you have a cleaning kit. This comes into the crafting territory. So for balancing game mechanics, having guns get gunked up due to dirty, possibly home made ammo after a few hundred rounds is fine, causing missfeeds and stovepipes, so long as it is not a case of throwing crazy money at a technician every time a gun needs a clean. Then on top of that, you have the useful service life of a gun. meaning parts are worn out, barrel is burned out and it needs to be scrapped this would be 10-50 thousand rounds, depending on the ammo used. So really you are looking at two separate "Health" values of a gun.
I have personally had feed issues with rifles due to quite minor dirt and damage. the main thing that tends to give problems is impact. Magazines are the worst, often giving problems. Then the mag release catch and then the gas system. The main thing here is; don't believe the hype. guns are machines. Most times they work fine. Other times they do not. When they do not, you better have a back-up plan.
Armour; Level 2-3 armour, meaning kevlar fabric, flexible armour is only any good against unjacketed rounds. So, 9mm, 45acp etc. handgun and sub machine gun ammo usually. It can stop a whole clip of the stuff just fine usually. multiple clips even. Against jacketed ammo, it does absolutely nothing. You might as well wrap yourself in tinfoil. 5.56, 7.62 etc walks through it, and would keep going through another three or four vests just like it.
Plate armour is either ceramic, which does break and become pretty useless after the first few rounds have hit it, or you can opt for thick sheets of solid hardened steel. This stuff you can shoot it all day and you will not go through with conventional ammo. The down-side is weight. It weighs a total ton. All that being said, being hit with a big bullet into a piece of plate armour will hurt a fair amount, and will likely knock you over.
Now, with all these real-world options, the trick comes down to which pieces to implement into game-play. Having armour which has a percentage of protection makes no sense at all. armour either works or it does not. Personally I think a mechanic where by, soft armour is lightest, enabling you to carry more in your pack, ceramic armour is second lightest, but breaks really quickly, and steel plate is the heaviest, using nearly all your weight allowance. The two plates stop everything. The soft armour only stops 9mm and 45acp, shotguns etc. 
I also would like to see a knock-down mechanic if you get hit with a calibre above 5.56ish. A 7.62x51 will knock you on your ass and feel like you were hit by a truck, regardless of your armour rating.
Also, with plates, you can choose to have one on your back, one on your front, or both.
Also, plates usually do not protect from side-shots, or gut shots.
Ok, just some ideas I thought I would throw out there.

After playing dayz a fair bit, I honestly feel this would be pointless. I mean imagine finding a really good rifle, only to behold that it's ruined. Just annoying in my eyes. I mean it would be realistic but it's a game.