I think you are being a tad restrictive in your definition. Would you rule out electronic pick-ups, or to play BG do the players have to gather around a single mic (my preference BTW, but no one has been inviting me to play in any large auditoriums!)?
I'm not against playing any kind of music any way you want (I think you get that). I'm arguing for the
preservation of terms we use to describe particular genres, so that the terms retain their usefulness. I'm frustrated sometimes when I use a correct term to describe something, only to find out that common usage has caused the term to lose its specificity.
When I first started playing Bluegrass in 1975, the "governing body" of Bluegrass restricted instrumentation to a specific set of instruments. I don't remember what the governing body was, but I would wager that it followed the wishes of Bill Monroe, a powerful but pretty crusty guy (he scolded me and my friends once for the way we were dancing - we "ruined the waltz").
My band warmed up for the New Grass Revival in 1975 or 76 (John Cowan was their bass guitarist). Of course they were great, but at the time it was not considered Bluegrass - they didn't play [traditional] bluegrass pieces, and they had (gasp) a bass guitar. And, judging from what they called their band, it wasn't really Bluegrass to them either. Last year, they were inducted into the "Bluegrass Music Hall of Fame," so obviously the "genre constraints" had loosened over 45+ years (or said hall of fame had run out of the more obvious candidates... halls of fame have to keep going, right?).
Regarding pickups - as I said, we all have to compromise sometimes. I'm not aware of any rule dictating what means of amplification can be used, and since a pickup is in effect a specialized microphone, I would be lenient should I be asked to rule on the matter (an unlikely event). But like you, I'll always
like the old-fashioned way better. It's harder to get that high, lonesome sound when you're wired up.