It seems that Star Wars: First Assault, a Lucasfilm-trademarked title that was discovered earlier in 2012 by Fusible, is an Xbox Live Arcade-bound game from LucasArts. The web designers of Gifted Apollo found the image after digging into Xbox.com and grabbing the cover art files associated with every XBLA game there (via NeoGAF).
LucasArts hasn't officially revealed anything bearing the title Star Wars: First Assault yet. Responding to a query from IGN, a Lucas rep wrote, "It's an exciting time at our company right now, however we don't have any announcements at this time."
The (possibly temp) cover art clearly shows Imperial Stormtroopers engaged in a firefight with what appear to be Rebel troops, which suggests that at least part of the game occurs during the series' Original Trilogy. The location they're fighting in is less clear, but the architecture suggests Naboo's Theed, first seen in Star Wars: Episode I - The Phantom Menace.
I think it's a safe bet that First Assault won't turn out to be a match-three puzzle game, but it's really all just guesswork at this point. Did you spot anything in the cover art that I didn't? What sort of game would you hope for First Assault to end up being?