Seager may not be untouchable, but he is their future at SS and the cost to even get the Dodgers to start listening (likely Miller plus Simmons) is way more than the Braves should be willing to pay. Peraza will be a significant downgrade from Simmons defensively, and I doubt he would be much of an upgrade offensively. I would rather just see the Braves resign Uribe at that point.
He's LHed anyways, and the Braves should be focusing on impact (not necessarily power) RHed bats. Guys like Susac, Tulo, Braun, Lucroy, and Starling Marte (as examples) are the types of guys they should be targeting. If the Braves package position players like CB and Peraza with some of the arms they have stockpiled, and are willing to take on entire contracts, they should be able to acquire a RHed bat to pair with Freeman in the middle of the order through 2017.