Next Generation has a fairly superficial interview with 2K Marin creative director Jordan Thomas about following up on BioShock.
Unfortunately, Thomas can't talk about the new project underway at 2K Marin, but it's not hard to extrapolate from this talk that it will leave considerable room for the player's self- expression freedom which, unusually for games, has not come at the expense of narrative in his past projects; both the Shalebridge Cradle and Fort Frolic are saturated with stories that reach the player obliquely, through the level design itself.
(I really like the idea of the player being able to create dynamic physical attachments Rube Goldberg machines of death!) says Thomas, talking vaguely of future ambitions that may or may not be realized in his new project. (Those little chains of intent, those little arcs of player creativity are better expressed by tools that plug into each other. BioShock has a really great first crop of that kind of thing, but in games I do in the future I'll want to generate much more of that maybe give the player the ability to steal superpowers from characters that are wandering around the world, or alter their behavior in ways that amount to more than just getting them to fight each other. There's a lot of potential real estate there.)