The way Intel bins their chips is an insane cost saver for yield issues. Apple doesn't bin chips which means they can't afford to have crappy yields, meaning their pre- and post-SiVal would already be working like crazy to have a tight performance delta on all their chips. Due to the way design works for these SoCs you wouldn't be able to just grab a perfect A8X and start running it at 2GHz. Nobody in PD would have had the job to make sure the chips meet timing at those freqs, and nobody would have tried to make sure temps work at those freqs. If you want an ARM-based MacBook, you need an entirely new team at Apple to design the chips. It would be a huge, separate effort from the Phone/Tablet/Watch chips being designed now. And the biggest reason? There's no problem with Intel. PPC was dead in the water when they decided to switch to x86, and had no future prospects. There aren't any market conditions pushing them to ARM-based laptops besides "well maybe they could".