I don't mean to reference A7 as an Apple fan here but rather to point that they have had great success doing exactly the opposite of what ARM was pushing. Two high performance cores instead of 4 or more mixed cores.
Frankly it looks like ARM is slightly back pedaling on big.LITTLE as they are now promoting the idea of two high performance cores supported by four low performance cores. My point is if Apples rush to idle techniques are viable and they appear to be, why bother with the low power cores at all? Save the transistors for other things and run one core for light duty and power up the other under heavy load. From all appearances the transistors used for the low power cores are wasted, especially when you consider the support logic required to manage all the switching and interfacing.
In the end I see big.LITTLE as a architectural mistake. I will be surprised if in five years it is anything more than an entry in the history books.