There's a countdown timer on Lionhead Studios' website. It seems that the website will see a refresh in a few days, but the text also hints that "other surprises are coming." Right now it's just a red button (hint?) and a timer.
Counting ahead from the given time, it seems that the counter will end during next week's Game Developers Conference. We know that Lionhead's Molyneux will be in attendance, as he will be co-hosting a panel later in the week. Perhaps something else is going on for March 5.
Fable 4? Or could there be a new title announcement in store for us? Perhaps something on a new platform? We'll be there at GDC next week, so stay tuned.