That would be an interesting AU, actually. Kushina and Gaara's father were estranged siblings. Kushina left Uzushio to succeed Mito, while her younger brother chose to emigrate to Suna to become a shinobi after the village fell rather than live in his sister's shadow.
We've seen with the zombie kages that the Yondaime Kazekage did love his family even if he was crappy at showing it. Who is to say he didn't love Kushina, even if he couldn't bring himself to show it until after her death? Now she's died for a village that was not her own, at the side of a man that outshined all of the other kages, including her little brother. Of course, that did not set well with him, nor did the discovery that Uzumaki Naruto was Kushina's replacement. Not only had Konoha stolen his sister, now they have taken his nephew, too. All of a sudden he has good reasons to both want a power to counter Konoha in Gaara and to want to see Konoha destroyed.
Fast forward to the Chuunin exams where Temari, as the oldest sibling, is entrusted with the knowledge of her cousin and the task of befriending him in the hopes of convincing him to defect to Suna when the time comes. (Obviously this is before Orochimaru replaces him.)