Well at least for screen renders you can make sure render threads stay on the big cores and with GCD you can use thread priorities to determine what to put on w

Well at least for screen renders you can make sure render threads stay on the big cores and with GCD you can use thread priorities to determine what to put on which core. iOS has concepts of active/inactive and is mostly a one-app-at-a-time os. They also have a well defined background processing modes and extension API. With all of this structure, I don't think it will be as hard as we think it will be.