The rumor is that they're making one. Personally, I feel like the sorta free roaming nature of Bioshock and Bioshock 2 would lend itself well to an MMO, particularly if there was a wide arrray of Plasmids. I don't know if I'd go so far as to pay a monthly, but I'd enjoy it. Anyone agree with that?

Nope. Rapture is good for a one-off experience, I don't want to stand in the middle of some creepy ass building and type "WTS" and "LFP". 

I dont think its gonna seriously happen lol.

" Nope. Rapture is good for a one-off experience, I don't want to stand in the middle of some creepy ass building and type "WTS" and "LFP".  "

You wouldn't get the same feeling of being alone with only you and the splicers...and some main story characters. 
 
 
That's a huge thing that affects the atmosphere of the game.

I feel that I would eventually get tired of the underwater city.

I'm not really into MMO's in the first place, so I guess I wouldnt play that, even thou it's Bioshock. Also, the only real reason I played Bioshock all the way through was because of the story. I don't find the gameplay all that enjoyable. I think it gets old a little too fast. But on the other hand, as an MMO gameplay might be tuned up a bit with new abilities and new weapons.
 
Anywasy, for now I would have to say pass...

But can't you characterize any world of Bioshock as being a miniature sandbox? One with a few side missions built into the world and a few main missions which you are pointed to? Couldn't an MMO just be a fully open world version of that model? Where there are tons of audio diaries and mad splicers roaming around the vast dead city? 
 
I could see plot working like this. You are a world superpower who has suddenly discovered rapture at the same time as your rivals. A little simple I suppose, but gets the job done, justifying multiple players and a basic rival faction. Plus, the idea can be that parts of Rapture are being indoctrinated under each Superpowers ideas.

Rapture is a nice place to visit but I wouldn't want to live there which is effectively what an MMO does.

Rapture is a one city thing. It better be one big damn city if it was made into an MMO.