The announcement which Chmielarz tweeted about will be for the first project under development at the new studio. So far, all we do know is that the first new project from the studio is said not to be a shooter. Nothing other than that has been confirmed on what The Astronauts are up to.
People Can Fly is best known for Painkiller as well as Bulletstorm, and these developers have a track record of producing very interesting stuff, so it could be at least one announcement that we should very much look forward to hearing about. No word yet on which platforms the new title is being targeted at, but rumors suggest that it will be a console as well as a PC title.