Even Microsoft isn't at one OS yet, they've already admitted that.
Then what is Windows 8? There's the touch part with the desktop part and it freaking sucks
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Problem with a unified OS is the bloat that it would bring. One solution does not fit all. The way it has developed over time with mobile (Intel) and super mobile (ARM) architectures works well. Over time I expect this to expand to Ultra mobile architectures - just a scaled down version of ARM.
History has shown that portable devices require super simple interfaces, optimised software and streamlined approach for mass adoption of the technology- i.e iOS and Android. This won't change, if anything software will have to get simpler for wearable tech.
EG: iPhone, iPad.
Desktop OS's don't need this, they are the garden shed, the tinkering in the garage type devices that are powerful, filled with ideas, messy file systems and workhorse devices. This OS needs to be functional, powerful and customisable.
E.G iMac, Mac Pro, Macbook.
This is where Apple can dominate, Microsoft have gone whole hog touch, it's simply a blinkered strategy and not suitable to the way anyone has ever worked.
One solution DOES NOT fit all! I love that sentence!