Kovid has made a beta version containing the new virtual library stuff. It is based on 0.9.27. The installation files can be found at
http://calibre-ebook.com/downloads/betas/.
The point of the beta is to be sure that I haven't broken anything when making these changes. It would be particularly helpful if you try the various plugins you use. Of course, usability comments are also welcome, keeping in mind the UI and design guidelines that Kovid laid out in
post 12.
The goal is to include this stuff in the next calibre release.