So does Intel Core ULV used on Haswell Macbook Air.
http://ark.intel.com/products/75033/Intel-Core-i5-4350U-Processor-3M-Cache-up-to-2_90-GHz
ARM is all about ultra low power that's why it's so popular. If you need to increase the clock and TDP on it to reach certain performance, I just don't see it has any edge over Intel Core in your case.
The point of this discussion is Apple saving costs by manufacturing their own CPU's.
How would Apple using Intel Haswell CPU's help Apple save costs, especially since the A7 is as fast as a low-end Haswell?
Apple will have to use their own CPUs to save costs for a cheap laptop.