I think with somewhat little effort, because you already have the functionality, you could add the ability for people to look at other peoples decks and then do "mock-up" changes to their decks based upon the inventory of those other peoples.

So I'm "Eric", I look at "Joe Blow's" deck. I decide I have an idea for him after also looking at "Joe Blow's" inventory. So I click some buttons to "mock-up edit" his own deck without actually changing it of course. What he gets is some identifier of his deck that "Eric" has proposed changes to his deck based upon his inventory.

then he can see my changes, communicate with me or people in forums he asked for help in, or just accept the changes and let it apply to his deck, or lastly to save it as a new deck.

make sense?

btw: love the sites inventory abilities!