I currently work on a system that gives every player their own deck of cards. The idea being that rhe player draw instead of roll. Every player gets their own favourite cards and abilities that trigger on specific cards or card types. For example every Ace is a critical success, every club (if that’s your color) deals double it’s value.
Have you looked at Deadlands? It’s a Western RPG system that uses playing cards. That works great for Deadlands because playing cards fit the setting, but I don’t know if that would apply to a fantasy system. Have you thought about using a Tarot deck instead to be more thematic and offer some interesting opportunities with the trump suit?