A potential macro or plugin to enable generating diff's between files on different but related Trac instances. One example might be two different Tracs corresponding to two separate branches of the same repository, possibly spread across different servers using a distributed version control system like Darcs, SVK, or Mercurial. This would be a nice companion to InterTrac.
First mentioned by cboos in the Comment thread of Trac Ticket #2086
This doesn't seem to have been implemented yet. Sorry for any confusion, but multiple CamelCase entries in related Comments were pointing to a blank page here, previously.