I would like the card database to be downloadable. It would help my inventorying process. I'd even consider becoming a premium member for it if the database was formatted correctly and had adequate information.

I am curious what information would be necessary for such a benefit to you. I can see many benefits in this as well, quite frankly. Obviously the cost (complete, rather than just converted), power, toughness, and color info would have to be included. But what about (printed and/or Oracle) card text?

I use a home-brew database myself, and it does quite a number things that deckbox currently doesn't match, many of which may be of limited use to most people here, but that are exceptionally valuable to me (game tracking and deck rating allow me to predict with some accuracy the probable success of decks going forward; more detailed search capabilities, including the capacity to search rulings, let me find exactly what I need; etc.).

I would also find such a feature an enticement to consider premium membership, though I would warn that it should only be available to people who purchase a full year, as otherwise people would buy a month, grab it all, and go.