I can definitely say that Win 8 will not be as much popular as XP, not even 7 coz 1 main change in the functioning is the absence/hidden nature of Start button which will annoy most of the PC and Laptop users.
We are used to the start button but Microsoft has went off a wrong way by removing it.
Actually you're probably not right, windows 8 is probably going to be way more popular than xp and 7. The ARM edition alone is going to be where most of it's popularity is gained, tablets are so popular now. Maybe a lot of people don't like the start button being removed but the focus is on the metro screen not the desktop. Most people who are anti-8 right now will probably end up using it anyway just like vista.
Look. I totally agree Windows 8 is good for tablets, and fits in well, blah, blah; but the fact of the matter is, it sucks for the desktop environment, especially to Windows power users.