Another possibility is a B-side album over the years. That could be cool but I doubt there are any unreleased tracks we haven’t heard yet.
There have been rumours over the years of unreleased tracks from various albums that never saw the light of day. I can't imagine they'd go back any further than SOAPF though. B-sides album would probably be better than SC/Battles, as the bonus songs on both of those albums were better than the ones they included as part of the main tracklist.
As Krofi-chan says though, it's probably just comic book bullshit.