Stage events at this year's Xbox 360 Great Appreciation Festival kick off at 16:00 with Cave's head of development Makoto Asada. It looks like Asada brought with him some sort of announcement, as the "Cave Matsuri" official Twitter was updated today with a pic of Asada and a statement, "It's almost time for the press announcement. I'm nervous!"
It's unclear if Asada is referring to the public stage event, or if Cave will be holding a private press announcement prior to the event. The public stage can be viewed live. Visit this page for details.