The single only advantage x86 has in low power devices is that as of right now it's being manufactured on a more advanced process. Tit-for-tat, same process node, x86 can't compete performance per watt with ARM, and I think when A15 cores hit, even still at 28nm, ARM SoC's will beat down medfield.
I think we're talking about two different things.
x86 isn't ready for tablets as we know them, MS is releasing one with an i5 and HD graphics, it's obviously going to be faster than the Nvidia based ARM one and more robust since that one will run RT while the i5 will run the full version. There is a cost though, which is heat, weight, and battery life.
What I'm saying is I'm not ruling out Intel. The current state of tablets is niche really, small simple tasks all of which a phone can do none of which are capable of actually replacing a laptop.
Here's the problem with tablets, at least for me.
What we want: A desktop in a tablet
What we currently have: An over sized phone
Why do we want a desktop in a tablet? x86
You want your computer in a tablet, you don't want your phone as a desktop.
Sure we're going to have to draw back the time line a bit, the hardware is a major problem right now. It uses too much power, and isn't powerful enough. The i5 they're putting into the full OS version of the Surface isn't going to do it. However tech as we know moves quickly, and this is the goal. An x86 processor, running a full blown desktop OS, with the power to push real applications.
I think that is the future of tablet like devices, a future in software - which imo x86 has a huge advantage.