> Yes, we have also seen it on many of our clients domains.

Same here.

Does anyone have operational experience with a scheme of labeling
envelope sender addresses to recognize legitimate bounces to own mail,
such as the BATV scheme (Bounce Address Tag Validation):

What does such a scheme break? Do any mailing list management sw
use envelope sender address for membership verification (instead of
using author address in a From header field, or maybe in Sender)?