Cave development head Makoto Asada recently said that he'd be announcing at least two new games before the end of this month. It looks like one of those announcements came today via a teaser site.
DoDonPachi Saidaioujou is presumably a new entry in the DoDonPachi series. The page does not contain any details as far as platform or release information goes, so we'll have to wait for official announcement.
This is the second time DoDonPachi has been in the news over the past week. Last week, Cave announced DoDonPachi games for iOS and Windows Phone.