The plan:

July 27, 2013 WordPress 3.8 announced as in development concurrently with WordPress 3.7
July 28, 2013 Kick-off at WordCamp San Francisco Hack Day.
August 7, 2013 Initial meeting to scope out the release. See here and here.
August 15, 2013 Feature Plugins kick off. See here and here.
November 4, 2013 Merge window opens.
November 13, 2013 Merge window closes.
November 20, 2013 Beta 1.
From this point on, no more commits for any new enhancements or feature requests in this release cycle, only bug fixes and inline documentation. Any enhancements/feature requests not completed and committed by this point can be resumed in just a few weeks at the start of WordPress 3.9.
November 27, 2013 Beta 2.
December 4, 2013 RC1.
December 5, 2013
December 9, 2013
Hard freeze; RC2.
December 12, 2013 Release of WordPress 3.8.

To get involved in WordPress core development, head on over to Trac and pick a 3.8 ticket. Need help? Check out the Core Contributor Handbook.

Get your patches done and submitted as soon as possible, then drum up people to test the patches and leave feedback on the ticket. As stated above, no patches for enhancements or feature requests will be committed after the posted deadlines, so that we can all focus on squashing bugs and hopefully deliver the most bug-free WordPress to date. Wish us luck!