ALL hardwares are getting faster and the phones will soon pass the 1Ghz range as the "norm." Which means if Win8 is like Win7 and they could streamline it to be speedy on a slow system, like Win7 in a Netbook, then Win8 should be able to run on Phones by the time it comes out in a year or two.
AS I have stated to everyone I know, Tablets will be the ONLY FORM FACTOR in some time. Just look at the way phones are working, they are all a SINGLE SCREEN. The people that say they hate tablets will soon be dead or close to it and the people that have taken the "Smart" Phone and use the HELL out of it will be the one taking the Tablets / Slates form factor and driving the market with it. Plus, hardware is getting faster and batteries are getting longer, it won't be long before we can run full desktop Windows on a handheld phone-sized PC.
Have fun with that.
Here's a cool link of what life will HOPEFULLY be like in about 10-20 years.
http://www.youtube.com/watch?v=6Cf7IL_eZ38 
