Isn't some sort of deism at least plausible and reasonable at this juncture?

That would majorly depend on what "deism" means, as a concrete model, other than "here my other models break down". After all, if you can postulate an intelligent and moral being, with exactly our own kind of intelligence and morality, with the power of creating a universe, then surely you can posit, with much more confidence, an unintelligent and amoral system with the power of creating a universe.

Is there a materialistic theory of what happened before the big bang that is worth putting any stock in?

There are many, but none of them are in the realm of testability due to the dependency to a flavor of quantum gravity. Let's not forget that the Big Bang is a singularity, meaning a point where the model breaks down and cry. If you want to go 'before' the Big Bang, you need a wider model (that is, a theory of quantum gravity).

Or are we in an agnostic wait-and-see mode regarding pre-big bang events?

That is surely the most sensible approach at our point in time.