I'm guessing that they'll do the safe thing and produce a Sins-2 though I'm not sure what it's selling point would be. A greatly improved online multiplayer system and interface with features that rival or improve upon Battlenet with built-in voice comm might be a selling point along with additional game types (some sort of Capture the Flag game) and more races and planet types.
Doubtful. The vast majority of sins players do not play online. If they really wanted to sell, they'd have to focus on single player aspects. Perhaps a very dynamic campaing. A campaign/scenario editor. Maybe a ship editor like spore but less cartoony. Then just have a far more detailed game. Things like more indepth diplomacy, more factions to choose from.
Just look at how big the modding community is. Imagine how popular it would be if they gave the average joe the tools to make a mod without needing 3dmax or XSI or having to fiddle with codes in notepad!
As awesome as multiplayer is, from a business stand point, that really wouldn't be a good area to focus on for a sequel ( ). With luck though, they'll produce a really detailed game with customization options and an enhanced multiplayer.