The question is how powerfull can that ASIC be and what is the power consumption?

The number of miners is absolutely irelevant, the minign power matters.

Ok how about this, lets say there will are 4 billion miners(which will never be because thats half of the world)

Can you tell me under your asumption what hashing power will that have asuming that there is a chip on thier phone that can do double-sha faster than normal general CPU.