By "xenharmonic" I mean music in a non-traditional well-defined tuning system. This is a narrower concept than "microtonal".

For example a song in 19edo or Bohlen Pierce would count as xenharmonic.

12edo or any traditional but non-Western tuning such as maqamat or ragas does not count. Harmonic seventh chords in a barbershop quartet doesn't count. A song that's mostly 12edo but with bending, slides, a few quarter notes, or a half-sharp modulation does not count. Simply playing/singing sharp or flat (either deliberately or by mistake) doesn't count. A violinist adjusting thirds and leading tones to their "just" equivalents in otherwise traditional music doesn't count.

If the song already charted before I posted this, but after 2000, that still counts.

Hopefully this definition is clear enough. I will only bet after one month of posting this, so that I can answer questions and clarify the criteria before I make a prediction.