Offering a value-bonus or a bonus in miles for buying a gift card now would not be crazy either; there might have to be some limits so that you don't turn around and buy a flight with it right away though.
Even if there were no restrictions on immediately booking a flight, it might still be worth it for Delta to offer a gift card bonus. Not everyone will immediately book a flight, and those that do have effectively waived their right for a cash refund if their flight is cancelled (it will go back on the gift card used to book the flight.) That's a pretty big benefit in terms of cash flow.