Ars Technica also has a nice 2010 article: http://arstechnica.com/information-technology/2010/06/the-be...
The way it implemented the queries well was because they were integrated into the filesystem. Windows/Mac/Linux do it in userspace. Doing it in the filesystem would be considered a layering violation by most.
For years I though he was secretly writing a BeFS like replacement to HFS.
APFS seems less ambitious however.