The main problem that was raised is that a failure in one library causes all the docs to disappear. No longer missing docs from problems in individual libraries.
There is a meaningful advantage to that "problem" though. Right now boostorg/pfr docs are failing. Peter and I commented to the author. This morning I submitted a bug fix which is just waiting to be merged. Imagine the alternative: a mostly-unmaintained library starts to have doc failures. The 'superproject' continues to build fine. Nobody sees the issue as particularly important. Perhaps someone notices, but think "it's that maintainer's responsibility". The next thing you know, it's time for a boost release and the library's docs will not be included in the official archive since they are not building. Which means, at minimum... set up persistent email notifications and show the build is failing somehow.