It will be native to Ivy Bridge so there is really no reason for Apple not to include it. They won't need a separate USB 3.0 controller. Don't expect them to drop Thunderbolt, however. They'll just have both USB 3.0 and Thunderbolt.
I think the main reason it isn't in the current products is that it would require a separate controller, and there isn't enough room in the current logic board. Apple, being a proponent of Thunderbolt, chose to use the space to support Thunderbolt rather than USB 3.0. If you notice, notebooks often have only 1 USB 3.0 port and 1 or 2 USB 2.0 ports, partly because right now, USB 3.0 requires a separate controller. With Ivy Bridge, the compromise is no longer necessary.