Agree with CarlowSEO.
Maybe not even gift cards but a new cart endpoint where the value of the cart can be modified. It will allow for a whole new range apps to be built including gift cards.
@Hege Hammersland-White - At least it's not just me that get's no reply to emails. This is my first ever experience of a company that just does not respond, no matter who I email or tweet within the company. It's very frustrating and very unprofessional. Maybe there's some month long holiday in Canada?
Anyway, I am going to do some research this week in to creating a gift card app. I'm aware that it's going to involve a few hacks. Do any merchants have any preference as to how the amount should be deducted across a basket? For example proportionately across all products or from a single product first etc.. The problem might be if you need to refund an item.