Re: Holland was clearly making a point..
Those users who need reply all should have the clear option of choosing it, or setting it as default.
For many organizations, that would be "all users". The snowballing-reply-all-conversation pattern is culturally entrenched in many places.
For the reset of the world, 'reply all' should default to BCC, and the target should reset to equal the sender.
Then each responder ends up adding everyone back in again. That's not an improvement.
I agree that email discussions among a dozen people are a poor way to communicate. But as I said, it's culturally entrenched in many places. Until you change the culture, there's little to be gained by changing the interface, except possibly to add confirmations with good heuristics (so users don't simply become trained to click through the confirmations).