In a thread on NeoGAF, user milkybar1983 posted a bunch of images of box art for upcoming Xbox Live Arcade titles. One such game is Star Wars: First Assault which, curiously enough, has not yet been announced. The cover art is even hosted on Xbox.com -- and it's still up, at the time of writing.
Earlier this year, trademarks and the StarWarsFirstAssault.com domain were discovered, so the game appears to be legitimate. After reaching out to LucasArts, IGN received a nicely crafted non-comment: "It is an exciting time at our company right now, however we don't have any announcements at this time."
The box art itself is suitably vague, unless there are some details one can draw from it that I'm just not picking up on. Now that the cat is out of the bag, we'll likely hear from LucasArts before too long.