Self-Validating Empirical Epistemology?

[Neo-Scholastic]

Technically, it is not an axiom because the counterfactual (not all propositions must be empirically verified) could be true. As an first principle it is self-refuting. It's actually an initial premise. While it serves as a good guide for doing natural science, it is worthless for establishing metaphysical claims such at the nature of being-as-such.

Not quite, Chad. The counterfactual statement would be 'The truthfulness of all propositions must not be empirically validated to count as knowledge'. As a statement, the individual words make sense but as a whole, it sentence has only grammatic veracity  
Consequently, the proposition can be held as axiomatic.

That's a disingenuous change because you are trading on the ambiguity of 'must'. In the original proposition 'must' means the same 'need'. Skeptics are claiming that people need to empirically verify something to know if it is true. That's not a self-evident statement. because it could be possible that there are some propositions that don't need to be verified to know they are true. We already have an example of one: the Principle of Non-Contradiction. Since the PNC requires no empirical verification, the other original proposition is false.