G4TV had a great retrospective on the System Shock franchise last year, describing it's links to the Dead Space series and why there probably won't be a System Shock 3 (and likely, no re-releases of System Shock 1 or 2 on Steam or GOG) any time soon, here's the link to the post: http://www.g4tv.com/thefeed/blog/post/713030/the-lost-history-of-system-shock/
Here's an interesting quote summarizing some of the issues:
if EA wanted to publish another System Shock, the company didn't have the rights to do so. Back when the original game was made, producer Warren Spector negotiated a deal in which EA got the trademark to the series, while the developers at Looking Glass Studios kept the rights. To create another System Shock game, you need both. "My thinking was it would force us to be married so it never would be that either party should be able to say we own that, we’re making the next game, screw you," Spector told the San Jose Mercury News last November.
In hindsight, the deal only jeopardized System Shock’s future. Looking Glass Studios closed in 2000, a year after System Shock 2's release, and the copyright to the series went into the hands of an insurance company. That left EA with only the System Shock name, but no actual development rights.