2K Games Teasing BioShock Announcement

It looks like 2K Games may have a new BioShock project cooking.

If a tweet by 2K United Kingdom is any indication, we may be taking a return trip to Rapture sometime in the not so distant future. The post contains the following picture, accompanied by the ambiguous description: "Oooo, what COULD this mean?!"
 

Fans of the franchise will recognize the image as an in-game ad taken straight from the original BioShock's underwater city, Rapture. Could 2K be hyping up a new entry in the series? The company has made it clear the BioShock franchise will continue despite the dissolution of Irrational Games, so that sounds like a fair assumption to me.