I can't do it, but the biggest thing I'd want to see are robust, intelligent bots that can be used in any game mode, but especially siege.
I'm talking Bots that will take leadership roles and issue orders or follow orders given by the "leader" (player so-designated). If you could spawn a bot of a specific class, that bot would know what to do on that map using that class, etc. More complex but even cooler would be bots that would use vehicles properly (including starfighters in Siege Destroyer2/asteroids).
That and fixing that "stuttering camera" bug for the swoop bikes on Siege_Destert and the "cloak stops working" bug Lando on the same map.
A lot of stuff can already be done in the game that doesn't require the source, but now that it's out, it seems the sky is the limit, though the number of modders with the time and talent to do it has really narrowed. I can understand it's tough to dedicate that kind of effort to a game that's considered so "old" but I hope somebody takes it up.
After all, this is still the best franchise of online Star Wars action games (unless you're a MMMO fan... but can you even mod those games?).