This is something I'm running into while trying to heavily modify a server for me and my friends. I'll cut right to it:
I use a skill tree mod that uses attributes to modify players when unlocking skills.
Having features of this mod like backstab damage multiplier or defense meter be tied to player attributes would be wonderful because it would allow configuration or changeability for people like me; but also not change the default experience for other users.

This game already uses attributes such as Armor Penetration but those are for weapons instead of players.

Also I'm not sure if you can use simple true/false values for player attributes, but also having parrying or dodging be toggle-able through these attributes would be cool, but I care more about being able to increase or decrease multipliers.

This has been my wish for a Totally Epic™ upgrade to the mod.