I will simply compile all the suggestions I thought was worthy and should definitely be implemented in the game itself. some forumers have suggested these stuff before. so yea.

1. Tourney system (On the Way)
2. Auction ("on the way") (part of me is hoping SC is used in auction instead of Gold)
3. Custom Meltdown Matches (possible future meltdown tourneys)
4. "Sell Extras" Button (an option to sell any extra copies of a card)
5. Visual effects on card effects such as protector
6. Foil Packs or Digital Booster Boxes with guaranteed Foils
7. Deck builder (better format)
8. Name Decks ("Amber likes DP" deck)
9. In -game chat lobby
10. Friend/guild Implimentation (KS reward on the way)
11. Ways to spend gold on something else other than cards.
12. Custom avatars (on the way)
13. Increasing Foil rate (some games double chances of pulling rare stuff during certain hours like 1 hour) [they obviously have increase sales of in-game currency during those times.
14. Lastly, I hope one day for a 3d fight and actual simulations. (One day when a billionaire spends a big load of money on this game)

If you have a suggestion you wish to eventually be part of the game, post away and let YOUR VOICES BE HEARD. =]