Roughly in order of precedence (the closer to the front of the file,
the more likely it'll be done before next release):

* Update the database infrastructure to allow other RDBMSes.

Improved (and perhaps integrated) Services and Enforcer plugins.

To be done as soon as someone with the necessary expertise is found to
help us:

* Finish the Infobot plugin.

Hard problems that won't get done until someone really wants to have
some fun:

* Redundant relaying -- having more than one bot handle relaying,
  where a secondary one will automatically take over if the first
  becomes incapacitated.

* Have the bot detect when other bots are in the channel responding
  to the same prefix character, and do something based on that.

* Unicode support.  Basically, we'd have to have a way to set the
  encoding for the server, and use unicode throughout internally.
  The real issue is how much it would affect the current code to
  switch it over to unicode, and what kind of burden it would put on
  plugin authors to deal with that issue.