GameGossip is reporting that Electronic Arts has re-filed the "System Shock 3" trademark to the United States Patent and Trademark Office. While this doesn't necessarily mean that they're actively pursuing development of another System Shock RPG, it does confirm that they're interested enough to keep the name available if they decide to proceed with it.
Unless Irrational Games were involved, though, would we even want to play a System Shock 3? My guess is that BioShock will be what we'd want System Shock 3 to be anyway.