Five is just the domain registrations that came up, its not confirmed to be the official name of QD's next title, but they are definitely at work on something. A few quotes from David Cage for your consideration:
“For our next project we’re going to build on what we have discovered with Heavy Rain. We own this genre of Interactive Drama and we want to show that Heavy Rain was not a coincidence; it is something that makes sense and we can build on it.
At the same time, we will not make a sequel and I made that very clear from the beginning, regardless of whether the game was a success or a failure, because I wanted to show that this is a new genre that you can use to tell any kind of story, in any style.”
“We’re going to be exploring a different direction, which will still be very dark and still for adults, but completely different to Heavy Rain. Our challenge is to satisfy our fans, and also surprise them.”
Also, following the Bafta success of Heavy Rain, Cage gave an interview with the Guardian in which he called on developers to draw on their personal experience when creating a game concept:
"Don't write about being a rookie soldier in WWII, because you don't have a clue what that's like. Talk about yourself, your life, your emotions, the people around you, what you like, what you hate – this is how the industry will make a huge step forwards. I'm fed up with space marines."
So there you go, no sequel, no space marines.
