I like this idea. I do not wish to detract from it, but in response to comments about it being too complicated or too easy to obtain recipe's etc, a possible simpler if not as nifty method would be more of a melting pot than forge. Open up pot, start selecting cards and when done click merge. Game would calculate value and rarity of cards and based on that spit out a card. The more value of cards the better card created. Occasionaly with enough value of cards it would produce a rare. You never get to choose the card. Tossing in a rare or upgraded card would almost gaurantee a rare.
Of the two ideas I defintely prefer the forge idea though. If the forge is put in play, maybe melting pot could be used to break down cards into materials?