If I knew how to make mods for UT2k3 and I actually felt it was worth investing in I would at least give it a shot at making a mod for UT2k3 to follow the alien breed series.
Sadly I only know Java, and I doubt that UT2k3 would run in that. Otherwise great idea. I know that there is a mod for UT which lets you play Unreal levels or create single player campaigns. I wonder if they'll port that to UT2k3. Then it'd be a matter of skinning, level designing and scripting
How about chaos engine. UT2k3 makes nice outdoor landscapes as well as far as I can see.