I think a good mechanism you could start off with is everyone who wants to play multiplayer can put 3 any cards that they'd like in a slot and whoever has them added can choose to use those three cards before they go into battle (: more of a supportive approach everyone's helping eachother and that will push towards getting more and more people to play, then that's when you start getting technical with hardcore online play, because for a card game you have to make EPIC prizes and cards for tournies, and a free card for a loss and two free cards for a win for just normal matches
just an opinion for you to look at(:
 "Clash of Cards"){kind=icon}
What a nice idea! Thanx! I will add it in my todo list.