From Norm Walsh http://norman.walsh.name/2005/10/28/docbook50b1:

"Although it's taken me a couple of weeks to get the release ready, at the 12 October 2005 DocBook Technical Committee Meeting, we approved publication of DocBook V5.0b1 as the first official (test) release of DocBook V5.0. I expect a fairly long series of “beta” releases to follow, then a series of “candidate releases”, before we get to an official V5.0, but we are at last on our way.