More content to encourage a community to grow.
Multiplayer space missions - Realistically on rails space missions are here to stay, but you can still improve it. Make it so you have multiple people controlling ships, make their paths intersect enough so that you have to watch each others backs, ramp up the difficulty etc.
Mini-Games: Pazaak, races, etc. Anything to encourage something beyond sitting motionless on the fleet surrounded by 17 others doing the same where no-one talks until someone comes on here to cry about a lack of community.
Legacy Mission - Doesn't have to be a huge amount of work, recycle and existing map (Say the governers mansion on Corellia) for a legacy mission, played once a week with a toon of your choice (and only once per week for entire legacy) you take a single player mission with your other legacy members as NPCs (think that trooper mission where your given all but your current companion as elites). Reward an inheritance piece of gear. Simple recycling of stuff that's already there. Looks like a new additon.