While Microsoft limits XBLA updates to just four megs, the fighter's Slightly Different Edition patch weighs in at 590 megabytes. Being granted an exception to the rule is apparently possible, though subsequently time consuming. No announcements have been made regarding an expected completion date for the whole deal.
Though dubbed Slightly Different, the patch changes an impressive number of details for each character in Skullgirls, in addition to adding further modes and UI improvements. It's also supposed to decrease load times, though the patch itself seems to be suffering from quite a long one.
Update: We were contacted by Lab Zero Games' Peter Bartholow, who clarified the situation a bit further. "We've been working with MS developer support and have managed to reduce the size of the update significantly," Bartholow said. He went on to inform us that the size of the update itself is "still in flux," but that Lab Zero is "hopeful that the size reduction will help speed up the submission process."