i would add a feature to the market that allows the seller to pick what currency they want for their card but the buyer can use whatever they want and splinterlands would exchange the currency's. for example say i want to sell a card for 10 cents and i want dec, and you want to buy that card and you want to use steem. then splinterlands would take 10 cents worth of your steem and then exchange that for 10 cents worth of dec and give that to me.