Email Feature: Reply All "Discouraged"

In email,  I feel like we need a middle ground between:

1. The standard open distribution list, that tends to encourage the default behavior of Reply All;
2. The bcc technique that prevents this, but makes it impossible both to see who is copied, and to Reply All if it is indeed appropriate.

So the Reply-All-Discouraged feature I envision would operate as follows: 

1. Have to be consciously invoked. Perhaps even explicitly enabled in user settings.
2. Set explicitly on a per-email basis. Sender could optionally provide explanatory rationale for when Reply All might be appropriate.
3. When a recipient clicks Reply All, they would get a pop-up with a generic explanation of the feature, and any explanatory text from the Sender.

While making this work universally would require a formal or informal standards change, I think Gmail and Outlook have enough market share to implement independently, and get significant value out of it. For out-of-platform recipients, it would have to default to bcc.