First thing that needs to happen is a to divide the card system into: First cosmetic cards and second loadout cards.
Then next system needs to be implemented:
Cosmetic cards:
Trading between players of cosmetic cards. You either sell a card for credits/real money and a certain percentage goes to Splash Damage/Nexon. Or you trade a card for an other card where you pay a certain fee to Splash Damage/Nexon to be able to do the trade.
Loadout cards:
Keeping the trade up system for loadouts, but with an extra final stage that lets you trade up 4 golds for 1 fully crafted card.