Bioshock fans - thoughts on a sequel? (spoilers)?

I was just finishing my second play through of Infinite. This game has blown me away - I've always loved Bioshock, and I think since that first glimpse of Rapture it's been one of my favourite series. Ken Levine is quite a genius and this is quite clearly seen in the development of characters and architecture of the stories throughout the games. The rest of the team at Irrational are also pretty incredible - the settings are amazing and the game play is dynamic and fairly unique, though I felt this area was the only way in which Infinite could have disappointed.

Having said that, the ending of infinite was incredible - a very good way to rap up the series; everything is tied together. The quantum stuff and the many worlds business kind of popped up out of nowhere, and no one can truly say whether it was planned all the while. I'd personally say no, because like a said the multiple universes stuff comes out of nowhere and is not mentioned before Infinite, but is literally the glue that holds everything together.

The point of this question is: the story is pretty well tied together. To revert back to rapture or Columbia or even a new setting would be difficult as the story would be difficult to enjoy when essentially, Infinite is already the Pinnacle of the series. What do you think they could do with a sequel to top Infinite, keep the game fresh and tie in completely with the previous games?

I personally think that the series needs to take a completely different direction. I was thinking perhaps an open world online game set in Rapture. Make it massive and continually expand it (much like the online content of the new GTA game). It could be a kind of multiplayer survival thing, with side quests and some events that tie everyone in together. Sort of like an RPG style thing. People could manufacture their own vigors/plasmids and weapons. The possibilities are infinite... pardon the pun.

Any ideas welcome! Would love to hear other fan's thoughts on this.