I honestly don't see Apple using the Tegra 3 in any of their idevices. Why would they, when they have their own ARM based Chip Design team. With that said, we already hear the rumors that the A5 (or A6 depending on which generation they switch), will have the Cortex-A9 processor which is the same processor used in the Tegra 3. Apple doesn't need to go to Nvidia to get a quad core processor for the iOS devices as they already have a team working with the very same processor. Secondly, the next gen GPU most likely used is the PowerVR 543. The 543 is also also capable of being multi-core and could push as much as 3x to 4x the video processing power as the current 535. I would also venture to guess that the 543 wouldn't require a complete rewrite to the drivers and software that will be utilized in it like the Tegra 3 would.
While the Tegra 3 is great, it is really no better than what is already rumored to be in the pipeline for future iOS devices and would require a lot of driver and programming changes for both Apple and Developers to implement.