The other option is buy an evga card then if something faster comes out you can use the step up program.
The only downside to this is a significant wait time at launch. It's a great perk and you can reserve a spot if you're within 90 days of purchase of your card, but I've never bought EVGA just because of it (step up). I do like EVGA a lot, because their CS is unparalleled. I've never found a company better than them in that respect or even remotely close. So that's usually why I buy, not because of step up. Although lately i've been more impressed by aftermarket cards by asus and others....the ACX is a good cooler but not the best for aftermarket (IMO). Anyway, step up is pretty limited.
Going back I remember the 680 had a tremendous wait time for those who opted for step up using the method you described. You can "reserve" you spot in line if you had purchased the prior card within 90 days from the reservation, but still, it was a pretty long wait.
I guess, if I were dead set on getting 800 series i'd just get that and not use step up. But it depends on how much one doesn't mind or minds waiting. If it's 30% faster than the 780ti and 500$ , there will be huge lines of people waiting for step up via reservation. We'll see I suppose.