Why not rebrand WP to Microsoft Spartan?

Because its now referring to the browser not an OS?
It throws a wrench into the entire "one Windows" idea too.
 
Hmm interesting idea. Not sure whether it's right or wrong.

The Windows name does bring brand recognition - but is that a good or bad association? I guess it depends on the person.

Perhaps a cool name like "Spartan" could allow it to distance itself from the "old IT guys office" name of Windows and be more appealing to the younger audience? Dunno
 
Being a college professor in a business school in a major metropolitan area who has run marketing research studies using students here and abroad as guinea pigs, I can confirm that there is a huge brand issue with Windows and Windows Phone with current generation college aged students.
 
There have been times where Windows has had a negative connotation. I think Microsoft has a chance to turn that around with Windows 10. As Xandros has said, Microsoft is banking on One Windows. I think they have a chance, there is plenty of positive feedback with Windows 10 Previews, and HoloLens is bringing a cool to the product that Microsoft has always lacked.

If there is a stigma about "Windows" from a younger, tech-savvy audience, they are smart enough to know that Windows is Microsoft. Dropping "Windows" won't solve the issue. Making Windows genuinely cool will.