There is very little information at this time, but it appears that Namco-Bandai has registered a trademark for a new game in the Soulcalibur franchise. The European trademark registration office website has revealed that a trademark has been filed for Soulcalibur: Unbreakable Soul.
There is pretty much zero information to tell us what this title will be from the trademark site. The only piece of interesting information is that the trademark was just filed about a week ago on September 27. Joystiq reached out to Namco-Bandai to see if they would confirm anything about the game, but they would not give a response.
If this turns out to be an actual game they are working, this would be at least the third Soulcalibur game in development by Namco-Bandai. They are already working on the previously announced Soulcalibur 2 HD remake and the free-to-play Soulcalibur: Lost Swords. As soon as some sort of official announcement is made about Soulcalibur: Unbreakable Soul, we will bring you an update.