Thing with this dual mounted gpus, amd or nvidia, if they use xfire/sli tech to show their performance, I'd personally still want to stick with the 1 gpu card.
Although it's all crammed on 1 pcb, or face to face mounted, to take up 1 physical card, once the case is closed, u may as well have 2 cards in there (if u have the room ofc).
Presenting itself as 1 gpu to the OS, then I'd show interest in x2 tech tbh.