Step by step the backend is near to be in a first release state. Today, it can load several Planner files and show them as different lists of tasks in Evolution and now, you can also add new Planner sources from Evolution GUI. In the screenshot you can see four Planner projects showing in Evolution.
I need to check now the really enterprise integration: using Planner Postgres database backend from Evolution. It is transparent for Evolution that project is in a file or in a database (libplanner does it), and with database, you have a multiuser backend, but we need to test scenarios and solve some concurrent access issues before thinking about sharing projects between manager using the database backend.
Three days ago I decide to update my Evolution CVS and have some problems with dependencies. I am thinking about if I will follow CVS Evolution or better, I will stop in Evolution release as soon as it has the plugin support for loading third party backends. It is fun to follow evolution day by day, as it is with GNOME and jhbuild, but you need a stable environment to develop and not loose time in solving environment issues.