The official Moodle development calendar is open to the public if you want to see where HQ and the community are in terms of the next release (2.9 which is due out in May). Each week is broken down to the general tasks, but more important milestones suchs code freeze, QA start, and documentation are all also charted.
The calendar is available here: https://email@example.com
And can be added to your own Google calendar by clicking the +Google Calendar icon in the bottom right hand corner.
Next event on deck? April 6th, 2015 2.9 code freeze begins (all new features will have been committed by that time). For more information on the roadmap check out https://docs.moodle.org/dev/Roadmap