To me the real problem with the 'God' concept, is that hardly anyone can keep the concept abstract. For those in the Christian West, the concept always seems to collapse into something awfully like the Christian god. This is a far more specific idea that fails Occam's Razor in discussions of this sort.
Some have suggested that God is simply all consciousnesses. In that respect, it would be impossible for there ever to be a separate entity called God, since each of our consciousnesses would form a part of that which we choose to label 'God'. It is important to clarify at this stage - I don't just refer to humans, nor just to those who inhabit a physical body, nor just to those who happen to be close to this particular planet. Nor indeed do I refer only to our idea of space-time. Whatever it is, consciousness seems independent of all these things, at least in the way we ordinarily understand them.