Can any guitarist tune normal tertian-stack chords on the fly at normal speed by pitch bending? It would be quite a trick. I'm not saying it can't be done, but I'd be curious to know who's actually done it. The usual fudge jazzers use is to damp the chords so fast you can't perceive much definite pitch at all except the attack.

The accompaniments you see in Scottish music books before 1800 are never power chords - sometimes bare octaves, otherwise they use only major and minor triads with a very occasional dominant seventh (which is is usually only on the very last cadence in the tune). And quite often a unison bass line which might be an invitation to improvise a thoroughbass, though keyboard instruments and harps were pretty rare in Scotland until the 1780s, lutes were extinct, and guitars were basically toys you'd never use along with real instruments, so there weren't many options for doing that.

I just had another look at Quantz. I hadn't noticed before that he's quite explicit about what he wants his fingerings and extra key to achieve: he says straight out that flats are always a comma higher than their nearest sharp. That remained the standard text on the flute for nearly 100 years. I also looked at Rameau's harmony book (1722) - no mention of equal temperament at all, only just ratios. And that was the most influential theoretical treatise of the entire century.

I also just checked out Charles Rosen's "The Classical Style". He has a lot of thoroughly unconvincing fluff about equal temperament in the 18th century, but the earliest solid example he comes up with is from one of Beethoven's late quartets: B-double-flat in the violin against A in the viola. Those had to be the same pitch class. But that's in the 1820s, and the reason Beethoven did it was wildly unlike anything in folk - the violin is playing in the minor while the viola is in the relative major.

I was once in a band with a fiddler like the one leeneia described. We ended up dissolving the band so we could reform a new one without her. Some fiddlers just seem to have missed their true vocation as chainsaw sculptors.