Compliments and a question

Congrats to Paul Erlich and Daniel Wolf for the EXTREMELY interesting
discussion regarding chromatic passages in Bach, Mozart and the later
romantics. I have NEVER in all the theory classes I took (and admittedly I
took too many of them) heard a discussion of chromatic runs from the point
of view of tuning (!!) However, I am a bit confused: it is clear that
such descending and ascending chromatic passages are not featured in Bach,
unless they are mostly chordal outlines. It makes sense that this could
partially be due to the tuning, although I had never thought of it before.
Certainly such even chromatic passages are common with Mozart, all over the
place. Would Don Giovanni still be in meantone?? When does 12-tET come
in?? Wouldn't Mozart be already in the "mechanical, even" tuning that P.
Erlich mentions in W.A. Mathieu's treatise??... did Mozart change his
style during his lifetime as the tuning progressed?? This wouldn't make
sense, though, since Don Giovanni is quite late in his output. (??? Ich
bin verloren...)

Joseph Pehrson