I wouldn't exactly call FTL travel a sci-fi plot device, especially in space based video games. it's more of an in general simple explanation for traveling long distances really quickly. In fact, most games tend to just gloss over the exact science of space travel, using travel animatics simply as a make shift loading screen.
If you're not going to make the passage of time (real time, not story time) an integral game mechanic, i'd avoid trying to go into crazy depth with the methods in which your character travel. Hell It may even be worth coming up with your own outlandish technology.