Now hear me out.
I get skills at the moment are still relatively new and needed of improvement but this I can see being something to be part of in the next major update or something.
I'll give a few examples.
If you want your "Fire Spell" to deal damage based on the user's stat "Defense" you can choose that, or you can use a custom stat like "Special" for a different type of stat for the attack stat but for skills. This I can 100% see be something useful.
(Note: I am aware you can use scripts to do this, however this type of stuff I find useful and you know sharing my ideas are always welcome!)