According to Watch Impress, Microsoft's going to release an 89Mb bit of DLC for Lost Odyssey on Thursday in Japan. We're reading this through machine translation, so don't blame us if it's a bit sketchy. It looks as though it's going to involve opening as area on the seabed in the fourth disc, and will cost 400 MS points. We're sure someone that can read Japanese will provide a proper translation soon enough.
No idea if this is coming to the west. Just dropped MS a mail.
Update: Here you go.