I certainly agree with the skepticism in regards to some aspects of string theory, and my impression is that skepticism is widely held. However, I don't think your interpretation of the extra dimensions of string theory is correct when you suggest that it would be possible to insert a God into them. The extra dimensions of string theory are tiny and curled up, not additional time-dimensions.
The other major flaw that I see in your argument is that you don't define God. If you posit that God exists, you need to define what that means, and what that God is. I put it to you that any such definition you could come up with would render the concept of God mundane and not divine, and thus would be irrelevant to any believer. You are of course welcome to disprove me on that point.
My point is not that people need to believe in the conclusions of the theory or even the theory itself, but that people would disagree with your definition of God to such an extent to render any such theory meaningless.
edit: I should also say that it is absolutely true that any theory that cannot be disproven experimentally is not a valid scientific theory but merely a hypothesis. All of the examples you give are hypotheses that, at some point, either an experiment was conceived to test them, or that still remain hypotheses. This doesn't mean that untestable hypotheses are worthless, but they do not qualify as scientific theories (yet).
I see your point on the string theory, I was claiming that as long as you have an untestable hypothesis you can construct and arbitrary route to get there. So pre-supposing an additional dimension which is orthognal to space time, would create a space which existed in all time.
"The other major flaw that I see in your argument is that you don't define God."
That is intentional actually, it reflects the challenge that any two people have when they try to define God, as a species there is lots of variability there. But it does not preclude one from creating a definiton, and then creating an untestable hypothesis around that definition (which is the basis of my rebuttal)
One could define 'God' to be a system, mechanism, or phenomena that exists in a dimension orthogonal to space time which is aware of and can interact with beings and matter which exist in the space time that we inhabit. But your later comment is more on the mark.
"I put it to you that any such definition you could come up with would render the concept of God mundane and not divine, and thus would be irrelevant to any believer."
This speaks to the question of 'who cares'? Which is to say that you have to be very careful not to conflate what a religion defines as God (or a god in the case of multi-theism) vs a physics theory which is about the nature of something which could explain observed phenomena associated with 'God'.
In attempt to disentangle the two, consider that we don't have a physics theory of 'consciousness' either, although we have good information about brain chemistry and construction. We can show that 'something' is missing because its possible to create a nearly exact simulation of a brain's physical and chemical signalling makeup and such constructions do not demonstrate consciousness. Such experiments tend to disfavor hypothese which hold that consciousness is an emergent property of the brain's construction or composition.
And to be clear here it is not my intention to create an 'escape through rhetorical trickery' (as I was once accused by a dogmatic believer) rather I think about these things as a means of trying to understand or to quantify my own feelings and experiences.
You remark "My point is not that people need to believe in the conclusions of the theory or even the theory itself, but that people would disagree with your definition of God to such an extent to render any such theory meaningless." seems to imply that for a theory of God to be correct that other people would have to believe the theory and agree with the definition.
I don't think this prequisite holds.I think the only thing you need to have a solid theory is to be able to make predictions and a way to run experiments to test those predictions. So the cosmological theory of God would show how the phenomena labelled as 'God' can do what it does. And then there would a philosophical discussion about whether or not the 'entity' known as God is an emergent property of the mechanism or something else entirely.
I am strongly reminded of Marvin Minsky's lament about 'Artificial Intelligence' where the study of AI has been unfairly criticized for 'not making any progress.' In his report on the progress of AI [1] he says "Artificial Intelligence, as a field of inquiry has been passing through a crisis of identity. As we see it, the problem stems from the tendency for the pursuit of technical methods to become detached from their original goals so that they follow a developmental pattern of their own." He observes that once we know how to do something we just go off and do it and as an engineering exercise it no longer meets the more meta definition of 'Artificial Intelligence.'
So we have computers that play chess (which was once considered a strong indicator of artificial intelligence) and we dismiss it as directed graph analysis. Etc.
My point is that one can create a hypothesis about how God exists (one that satisfies popular properties of God like 'everywhere and everywhen at once') only to find that once its clear then its no longer 'divine or miraculous.' I was always amused by the ancient aliens hyphothesis (effectively a God theory in my mind) since if it was aliens doing things we already know how to do which were considered miracles by people who didn't know how to do them were we all duped?
Once you understand the physics of how God could exist then the question becomes one of motiviation and philosophy. This is why I carefully separate 'religion' which is a series of commandments which generally apply to 'believers' with built in penalties that apply to 'heathens' with the question of whether or not God might exist.
The other major flaw that I see in your argument is that you don't define God. If you posit that God exists, you need to define what that means, and what that God is. I put it to you that any such definition you could come up with would render the concept of God mundane and not divine, and thus would be irrelevant to any believer. You are of course welcome to disprove me on that point.
My point is not that people need to believe in the conclusions of the theory or even the theory itself, but that people would disagree with your definition of God to such an extent to render any such theory meaningless.
edit: I should also say that it is absolutely true that any theory that cannot be disproven experimentally is not a valid scientific theory but merely a hypothesis. All of the examples you give are hypotheses that, at some point, either an experiment was conceived to test them, or that still remain hypotheses. This doesn't mean that untestable hypotheses are worthless, but they do not qualify as scientific theories (yet).