Hey Nils
Yea actually it would mean download all (or some of them) the public ones created by the deckstats users.
It could be a possibility to try to create applications that would search for decks that cover the own collection.
But if it's too much load to sync all those deck (maybe once a day during the night) than I can understand that ;-)
edit: Actually all the card information wouldn't be necessary if you're using the official card ids from the mtg-api. Then only the id and the amount would be sufficient.