a new equipped slot, that adds in class stones (think job stones from ff 14)
some example effects
-mage, frost to add a armor brittle debuff (bonus damage for team), fire to add a dot, lightning for a stun, earth to slow enemy attacks, air to speed your teams attacks
-archer, multi-shot would be cool, where it'll hit 1-4 times per shot fired, rapid fire where it halves time to shoot, poison tipped arrows for a dot
-melee, flurry of blows hits 4-6 times at half damage (only usable with spear), power strike / takes longer to swing but hits for more damage (useable by club/hammer), dual wield lets you replace your shield with a second weapon (both hit at 80% speed but have their own swing bars (so could have a crush and stab or something)), sunder armor usable by longsword and applies similar debuff as frost
open to suggestions and numbers not really balanced... just throwing the idea at the wall to be further brainstormed and maybe bits of it used
honestly biggest part i like of it is the mage elemental damages... makes them differ from ranged and as good as melee, and mages should be big power hitters comparatively we use magic after all lol