10 years? I doubt Apple will still be in the business of selling Macs in 5 years, at the rate iOS devices are growing.
Face it - for most of the stuff people do with computers, tablets are a fundamentally superior solution. Browsing, watching YouTube, updating Facebook - all best done from an iPad (or an iPhone, which is with you literally everywhere).
Desktop and even laptop PCs are only going to be really needed by business people, and even then only at the office. In fact, I'm not even sure most of them will need a PC - if the iPhone gains the ability to dock and work with external monitors and keyboards, it could function as your desktop PC as well (and as your laptop, with a mobile dock equipped with a keyboard, monitor and larger battery).
Any processing job the mobile device can't handle will simply be offloaded to the cloud, OnLive style. That's already practical in most offices, with their high-speed networks and fat internet pipes. It'll become increasingly practical in the home as well over the next decade.
The PC and laptop as we've grown to know them are as obsolete as the buggywhip. Apple won't be making an ARM-based MacBook because by the time that becomes worth the hassle, they won't be making desktop and laptop computers anymore. The form factors are totally obsolete.