It contains two new plugin types, one for configuration interface, and one for query cache. Those two are not "plumbed in", and are in fact just templates, containing two dummy entry points with two dummy parameters. But they follow the evolving pattern for plugin types.
It also contains fixes and improvements for the logging and errmsg plugins. The logging engine implementation has parameters for filtering for slow queries and for "big queries", both ones that return a lot of rows, and ones that just examine a lot of rows.
It's all also been internationalized.
There is still lots of work to be done, but it's fun to get this foundation stuff going.
I just read that Toru has a branch he's been working on a query cache plugin interface as well, so we need to work together to stitch all our work together.