What if Blizzard added a system whereby failed attempts increased your chances of getting a piece of loot via bonus roll when you finally downed the boss?
For you people who leave groups at the first sign of trouble, would this entice you to stay? Say you got 5% per stack or something of that sort, would you be willing to stick with it through the wipes, help the group, etc., knowing that after 10 wipes you would be at 10 stacks would have a 50% increased chance of getting loot via a bonus roll?
This is more aimed at pugs, even though guild groups would obviously benefit from it as well. And I guess such a system could theoretically be exploited if you could convince your group to get the boss to 50% or whatever the threshold for a stack would be and then intentionally wipe over and over, which I doubt people would be willing to do.
If such a system existed, I would think it would be prudent that it was character specific, so you aren't punished if you join a different group or don't get the boss down in one night, etc...
I see this more as rewarding persistence than rewarding failure, for those who might see it as the latter.