What's the difference between a non-stable branch as you're suggesting and the existing sandbox? The only difference I could see is to establish some kind of pre-review process. But that would just move the problem to a different spot, no?
The "non-stable" branch would be for libraries that have requested reviews or for "approved" libraries that have not yet stabilized. The "sand-box" branch would be for all other libraries that either have not requested reviews or don't plan to. The "review-wizards" John or Ronald or any of the "boost-moderators" could monitor the "non-stable" branch. This would clear the review queue. The only important review would be to establish when a particular library has achieved sufficient maturity to be moved from the "non-stable" branch to the "stable" branch. Once a library is in the "non-stable" branch, the library could be reviewed by anyone anytime. There would be no need for scheduled reviews, like we've had, although they could still be done, if the review manager wants to schedule it. The reviews would be ongoing and done in a blog format, not limited to a ten day block of time. After a library has been in the "non-stable" branch for say six months, the review manager could posts its progress to the mailing list and pose questions to elicit more feedback. The "non-stable" branch would be included as part of the boost installation, but only an optional part, not required. If a library is distributed as "non-stable", it should get lots and lots of attention. Nothing focuses an authors mind more than if they know that their library is going to get some exposure. The libraries in the review queue are not getting the exposure that they need, and are just sitting there for 6-18 months. Very few people are actually aware of these libraries. A better job needs to done to elicit feedback from domain experts. Having only a 10 day review period is way to short. It needs to be like 6-12 months, where the domain experts can contribute at their leisure. This could best be done if a "non-stable" branch is created, which is distributed along with the "stable" branch.