I've been able, for a short while, to refrain from thinking in this way, but the incredibly impressive ways that the DMS, wiki, and calendar have quickly been ported to Moodle makes me think about other PHP open-source software that have features that would be cool for Moodle.
Others probably have better ideas, but I've recently been enjoying dotproject. Specifically, it might be interesting to pull their tickets and tasks modules over. Both might be overkill, but having tasks (to do's) would be interesting in an educational environment and if the ticket module is robust enough (and I'm not sure it is), it might serve as the tracker that Martin has been sniffing around for.
I'm also still very interested in ways that blogging can replace journals (when journals become a subset of assignments). In particular, I think b2 evolution and Wordpress are excellent candidates. While RSS feeds and stuff might be interesting within a Moodle blog, all the pinging and trackback stuff seem unnecessary...
Finally, I'd like to find a "postnuke kind of module" that will allow an editor (teacher or student) to collect articles and to arrange them in some kind of on-line publication. See this.
Steal an eye here, a nose from there, digging into other projects seems like a lot of fun. Again, I'm only tossing out these ideas because people have done such a nice job of assimilating other code into the Moodle idea. Resistance is futile, Moodle is the superior collective.