We're considering various options (like using a combination of trac and github, or trac with a git plugin).  The following are some features we would like in whatever system we choose.

 * Everything is possible through an e-mail interface
 * Inline code comments
 * Easy hosting and low administrative effort
 * User-editable e-mail subscriptions based on component, file, keywords....
 * Ability to delete your own patches and edit your own comments
 * Ability to request a reviewer
 * Currently in trac (0.11) if you're working on a comment and someone else makes a comment before you post, you need to manually resubmit after an initial failure
 * The flexibility to add our own fields, like dependencies
 * Easy for current developers to transition, easy for new developers to get involved.
 * Useful reports
 * We should have options if our hosting service goes down
 * There should be ways to migrate to another system if we choose to move again
 * Integration between trac server and source control
 * Integration with patchbot
 * Programmable API -- easy for us to interface with our own scripts
 * Inline comments are preserved locally

Various options we've considered:

 * Trac + Github
 * Trac + Inline comments plugin + Git plugin