I am feeling uncomfortable with a few of the terms you employed. More precisely, the fact a model is complete has nothing to do with the fact it is observed or not. Many complete models are still waiting for an experimental confirmation (and they are kind of incompatible with each other). The word 'complete' has here a very well-defined meaning (in the context of model building).

Now on a more personal basis, I believe we don't necessarily need to get to the theory of everything in one step (there re conceptual issues there, in particular in the way gravity could be incorporated). We could aim to something extending the Standard Model at high energy, and then something extending the extension at much larger energy (and so on).