We haven't heard of this Siren in the Maelstorm. What the heck is it? "Silicon Knights is busy working on several exciting projects," a spokesperson told game site Eurogamer. "Unfortunately, it is too early to disclose any details."
Then, we shall wait.
Besides Too Human, Silicon Knights has also developed Metal Gear Solid: The Twin Snakes, Eternal Darkness and now "several exciting projects".
Silicon Knights quiet on Siren name News [Eurogamer]