Not sure how much more aggressive they can be. Their die size is almost twice that of the closest competitor... and they are using GPUs that no one else does.
As long as the process is mature, the die size really doesn't matter. It certainly adds to their cost, but unless they're getting loads of defective parts, they probably don't care too much if they need to spend an extra few dollars per SoC since their margins are so high.
At any given time, most of the SoC isn't actually doing anything so it's not as though making a bigger die is going to make it drain the battery like crazy either. Given that adding some highly specialized hardware can actually save energy by allowing the CPU cores to stay off, building bigger might have some tangible power benefits.
The GPU power is getting a little egregious, and it will be interesting to see how much of a performance bump comes from switching over the 600 series GPUs when they become available. If anything, that will probably allow Apple to shrink their die back down while still maintaining similar performance levels. Either that or they'll just use the extra space to cram in even more stuff than before.
Since they bought up all of those 4G patents, I also wonder if they're planning on making their own cellular radio and baseband parts in the future and adding some of that in to the SoC like Qualcomm has done.