I actually did hear rumors that Bethesda has been working on a game for quite some time, that uses the same engine that they used for Oblivion, Fallout 3, and Fallout NV.
But there is no real information about what it will be. People are hoping it will be a new Elder Scrolls, since it has been, what, over 5 years since Oblivion.
A new Elder Scrolls is quite due to be made now.
But who knows, it might be a totally new franchise. Maybe something set in modern universe; since Elder Scrolls is in a medieval universe, and Fallout is in a retro-futuristic universe. Would be interesting.