It’s to add content in the form of more maps such as Groves, floors of Citadel Station, and Cyberspace content.

Now, the 1.4m stretch goal is something much safer for us to scale if we don’t make the goal. We have an awesome vision for the game and setting a bunch of features we deeply believe in to a stretch goal stifles our own creativity since we can't fully plan for things. That lead to a bit of confusion and unease with our backers, and to be perfectly honest, deep system features like that are pretty dangerous as stretch goals. Before, it was vague and misleading regarding “RPG Elements”. We've altered the 1.4m stretch goal to something a bit more manageable from a game development standpoint. We’re hoping to having it some time next week if all goes well. Looks like the 1.1m stretch goal has been reached and we'll be supporting Linux and Mac versions of the game! Thank you all so much for making that possible! :-D We're working on bringing the demo onto OSX, but no concrete release date for it just yet.

System shock 3 trailer