So it's not exactly removing the notices, and we would not do it if the
affected entity formally objected to it. The reason I'm asking is that
it seems to be the only practical way to operate, since some entities
already declared that they agree with it only if *all* copyright notices
are moved.

I'm curious if anyone here knows legal reasons why it makes sense to provide this restriction ("don't remove my notice unless you remove all other notices from the file as well"). It sounds fair, but since no notice is required to retain copyright I'm not sure I really "get" it.