If you can’t measure a continuous thickness parameter throughout the test cycle perhaps you could measure a (somewhat) continuous abrasiveness parameter, trying different grits to see how quickly they wear through a standard coating sample (presuming you can reliably create those).

If you’re lucky there will be some sort of predictable relationship between grit and wear-through time, at least for given types (but not thicknesses) of coatings.

Finding that would allow you to accelerate your test with more aggressive grit and reliably predict the results that your initial standard grit would produce. You might need to come up with a standard “abraded material removal” protocol, too, so that effects from abraded material clogging the grit could be consistent.

HTH,
Jeff