I found that in another forum, could be only a big rumor:
Epic just announced that they are currently working on a second bonus pack for UT2003.
The second bonus pack will contain at least the following:
* 3 New deathmatch maps
* 2 New CTF maps
* 3 New bombing run maps
* 3 New double domination maps
* New player models: Skaarj, Nali and Nali cow
* New gametypes: (Team) Hunt, players have to hunt down a nali rabbit, and in the team variant they have to return it to their base
* New mutator: Darkmatch, every player is equiped with a flash light and plays in almost completely dark maps
* New weapon: Spider bombs, aim for a player and release the spider bomb, it will then chase that player and explode on impact
No word on when it's done or what the current status is.