Touch Mac OS X would kill iPad range and or will be prohibitively expensive. Microsoft OS has done clean integration of touch interface without making it as a big deal. Whereas Mac OS X would make song and dance of it to charge another $1000 more which no one would be interested in a product line that is failing in the portfolio.
Apple has to reinvent itself by challenging their whole execution by optimising their costs that must reflected where any increase in price must be completely unavoidable. Hereafter any random price increases won't be greeted with more sales...
Well, aren’t they looking to integrate iOS and OS X together? If it’s one unified OS, they could possibly be able to sell multiple form factors.
At some point, product lines die out. Chromebook 2 in 1s use Android apps and can be quite light. They make owning a tablet redundant if the portability is there.
I remember Microsoft might try a Surface Phone. I think a small display with x86 wouldn’t make much sense. But now? We have folding screens that could propel a Surface Phone into a reality. That could really hurt individual phones because they don’t have the form factor to compete with a hybrid model. But all of that is in theory, so I’ll wait to see how tech evolves before getting behind the folding screen bandwagon.