The future of Windows upgrades

Do you guys think that Microsoft will sell upgrades through the Windows Store? This would make sense considering that Apple has been doing the same since Lion. Or do you think that Windows Blue will just be a free service pack with more features than usual? I personally believe that Microsoft is going to offer it as a free update to prevent another extended life-cycle as with XP. On a side note, I think the next version of Windows will run on the Xbox, ARM tablets, x86 PCs, and phones, creating a unified app-development platform. Give your opinion in the comments below!