> the likely feedback effects on the broader economy that a universal rollout would have

It's interesting to describe as "likely" something for which there is no evidence. This is an actively anti-science belief. It seems to me as if you really don't like the idea of UBI and so are saying that, if it actually happened, the effect would be the opposite of what experimental data shows. This is pretty clearly biased.

> (increase in the money supply)

There is no effect on money supply if this is funded through taxes.

> Some things just can't be tested ahead of time empirically.

You can gradually expand the pool of people receiving UBI to see how these effects scale. Begin in one city, then increase to a larger region, then do it nationally.