All in all, I wouldn’t be surprised if all this is the price of the curse working its magic and soon it will rear its head for Snow who THOUGHT she could cast it and not pay a price. Heck, maybe that’s why Maleficent is coming back. Rump may have created it but only Maleficent knows much about it and Regina may seek her out to see if there is a way to cease the hole. or something.
My theory is that (a) we will see something come of the whole heart-sharing thing at some point and more importantly (b) Snow cast the curse with good intentions rather than evil, and the heart to be sacrificed was given willingly out of love–so perhaps she never had that hole in her (half of a) heart. I’d be perfectly okay with that explanation myself; it makes more sense than some of the other stuff we’ve seen on the show, haha.