Will. Not. Ever. Happen.
Not like that anyway.
I would buy one, but I can't because Apple won't make it. OS X is not currently well suited to touch. A more newton-sized iPhone is 10,000% more likely, and that will never happen either. If it does, I'll steal someones sunday hat and eat it.
They're more likely to do something like this:

That's within the realms of possibility in the next few years.