There's no official word on what it is, exactly, but Tower Records' preorder page has the most information. It's a 3-track single and all of the songs are Halloween related.
This is fantastic and I'm super excited considering how good Kerguelen was. Shockingly (?) enough, they're not releasing it on Avex but an indies label (not self-published, however, like Kerguelen was). As to why AV are no longer releasing things on Avex remains a mystery.