I have another suggestion too...
I think that the message below the download tag should be set by the addon reviewer, and reflect the actual status of the add-on
Let the default status message for an add-on that a developer has not requested for review, state the same fact... "This add-on has not been reviewed by Mozilla"
But when a add-on reviewer rejects an add-on from public listing, he/she always
informs the add-on developer about the reason for retaining the add-on in sandbox. I think this information is really, really useful, and should be made available as the status message of the add-on below the "Download Now" button. Because informing AMO visitors to an add-on page that "This add-on has not been reviewed by Mozilla" while in reality, the add-on has actually been reviewed (and found to be faulty or not worthy of public listing) is saying way too little and actually false in a sense.
Please instead inform something, like:
"This add-on has been not been approved as a public addon by Mozilla, because it has...
1) loose JS variables and can cause a conflict with other other add-ons, or...
2) we feel that this add-on is meant for a limited audience and has a very small active users base as of now, or...
3) etc, etc. (The add-on editors and developers can fill up more such reasons here, based on their experience
Coming to an actual example, just check out the info below. It communicates so much info that would be highly valuable in giving a better picture of the consequences of installing an addon to an add-on user:
Comments: Dear add-on developer,
It is unclear to us at this time if your add-on will be useful for a general audience so that it warrants public listing. We're rejecting your nomination, but encourage you to promote your listing so that it garners more active users and user reviews. You may re-nominate your add-on once there is more proof of its usefulness.