I personally really like the idea of giving weapons durability like shields. It would totally change how weapons were used and battles fought in the game. But there is a problem: The one with the big, heavy weapon would be at a gross advantage regardless of skill, and as someone said somewhere, lone superfighters would lose out against the endless masses of goons as their weapon slowly wears down.
The solution would be a parrying mechanic IMO. I don't know jack about coding a game, but I think I've figured out a way to implement this in a very easy, non-invasive way, and would love some critical feedback.
Outline:
1) Enemy attacks
2) You time your block as normal and holds down the button
3) Depending on a trait-based trigger, you have a chance to make a parry rather than a static block
4) Parry animation is triggered in your character model, while a Deflected Attack animation is triggered in the enemy
5) While the Deflected Attack animation lasts, the enemy is open for riposte from you
Now, some specifics:
There would be no need for any fancy physics or cut-scene like animations. Simply four new animations for each weapon type. When an opponent strikes at your head with his sword now, you see an animation of your own weapon going over your head in a horizontal line, stopping the attack from impacting. With this system, you instead see your weapon tilting downwards to the left (preferrably accompanied with a sound cue of some sort to let you know you parried successfully) and an animation of the enemy's attack having been redirected, perhaps something generic, like their weapon bouncing back (just to keep it simple), while your own weapon is now ready to riposte while he is momentarily stunned as the Deflected Attack animation plays. As an example. There would obviously need to be at least one Deflected Attack animation per weapon type, and four Parry animations, one for each angle of attack.
As for how it would be triggered, I was thinking of something like a percentage chance equal to 0,25 % for every point of Weapon Proficiency you beat your opponent by. But it could be handled as a separate skill too.
If the parry doesn't kick in, a regular block is made, with corresponding damage to your weapon.
Of course, for the sake of simplicity, there would be no guarantee of the two animations even making physical contact with each other. You might well see your axe aimed at the enemy's head be bounced back by a Parry animation that didn't even make contact. The animations would just be cues for mechanical effects. We can hardly expect a fencing system from M&B that even hyped-up, big budget games cannot do.
That way, we would be rid of peasants using clubs to block our great axes without making big weapons the be-all end-all of combat. And make combat way more interesting in the process. And I think it would be very doable, the new animations being the only real problem. Calculating the effects of Weapon Proficiencies in real time is done already, and otherwise, it would be a mere matter of replacing Block animations with Parry animations in the defender, and Injured animations with Attack Deflected animations in the attacker.