Some extensions are not specifically planned for the initial Beta feature, but do appear on the RecentChanges and/or Watchlist page.
There is full backwards compatibility for these hooks, but we should still move them into the new UI at some point.
There are also CleanChanges (not currently WMF-deployed, but it is in wmf-config) and WikimediaIncubator (WMF-deployed) that define filters that do not seem to fit in the current structure.