"ultra low power x86"
There's the problem in a nutshell. Intel has never been able to develop satisfactory low power x86, let alone ultra low power. Their best efforts at low-power have produced exceptionally low performance as well.
This might have something to do with their penchant for trying to solve issues by increasing complexity (much like a certain software company they have close ties with, which coincidentally is also having trouble getting its software to run efficiently on smaller devices.) In the low-power world, complexity kills.
Don't get me wrong -- Intel's x86 team does some amazing engineering, but its core design philosophy is antithetical to the simple requirements of low-power systems.