Just started playing elements - loving it.
Some ideas that I haven't seen on here so far:
1) In a PvP (either random or if you have chosen to play a particular person), be able to lay down a bet, be-it coin or possibly a random card from your deck. I currently PvP with some people in an IRC chatroom I'm in, and it would be great to be able to raise the stakes with some coin on the table.
2) Player groups. Again, I play with some people in an IRC chat room. It would be great if there was a common place in game where I could see all those people, check to see if they were online, and challenge them. (This could also lead to clans)
3) Be able to send other players coin/cards. Even without a full blown trading system, just this simple ability would enable trade to start.
Anyway, apologies if these have been mentioned before, but I thought I would bring them up if they haven't.