We should all keep two things in mind:
1) The dots are not the music, they are a code that allows us to perform the music.
2) Conventional musical notation is far weaker in communicating rhythm than pitch.
As to the essential nature of 6/8, it's interesting that Afro-blue came up as I have recently performed a chart of this with a big band. The chart is notated in 6/8. In a big band there are four sections: trumpets, trombones, saxes, and rhythm. In the chart I'm discussing, there are numerous sections where (for example) the rhythm section is playing in TWO and the saxes in THREE, or vice versa, and there are also long sections where some or all of the sections are playing in ONE (or SIX).
Strict adherence to the rules of notation would probably require constant shifting back and forth among time signatures, and maybe even sometimes the rhythm section seeing 3/4 (because they're playing in THREE for two measures) while the brass are seeing 6/8 ( because they are playing in TWO) and the saxes something else (because they're playing long strings of unaccented eighths). Well, that might be theoretically correct and satisfying to your college theory professor, but in the real world of musicians trying to read the chart, it would be nuts and anyone who brought a chart with all those time signature changes in, would be told "take this sh***T away and burn it!" In actual practice, whoever arranged this chart just put the whole thing in 6/8 and used the forbidden methods of beaming notes together and using phrase marks to indicate whether a particular measure was in ONE or TWO or THREE.
So the upshot of all this is that I am opposed to people issuing dictates about what MUST or MUST NOT be done in notation. If your musicians can read it at sight and interpret it correctly, then that's what you do. Personally, if I were writing out a passage in putative 6/8 that went back and forth between two and three, I most certainly would not switch it back and forth between 6/8 and 3/4 constantly. I'd probably use the beaming patterns of the eighths, or ties, or phrase/slur marks. I might get flunked in the college course, but the musicians would be able to read it, and that's what I'm interested in when I write music.
It's the same thing as "courtesy accidentals". Yes, we all know that the B natural you've been playing for six bars under an F major key signature expires at the end of each bar, but is your theoretical correctness really so important that you can't bring yourself to put that one little flat sign when the chord changes and it goes back to B flat? Is showing that you're CORRECT DAMN IT more important than helping the musician play the music right?
