Make the game intersting - LIve Rapture ...
I think I had in my above mass of text Ive written mentioning 'role-playing' Splicers and Big Daddies (even Fly-bots) as a possible expansion of my basic game (and intended a whole PvP sub-game to expand the MMORPG activities to keep a segment of the players happy).
Depending on how much freedom the players had to create stuff, they could be the ones to add such a mod (if the company didn't). MMORPGs should have more than just the fighting, and enough other activities (appropriate to the Rapture setting and the Classes) to fill in the playing time.
Interacting with NPC Splicers/Daddies/Lil Sisters etc.. would fill in some of that activity as well, as with a slightly more detailed Rapture terrain (salvaging stuff would be a matter of survival in that world)
The player interactions (cooperative) add alot to such a game and the faction dynamic would expand that (and give more goals the players can work towards) The time period could be just after the BS2 time, so that the small Factions/individual would be given alot of freedom to do their own thing (without interference of the 'big fish' Ryan/Atlas/Lamb )
The map should be pretty large (another reason to have player modding to help fill that out without some crappy repetitive auto-generation).
As alternative to my MMORPG (which is probably a longshot) would be REAL Modding the game --- which if 2K was clever would include a Server addition that would allow players to run continuous persistant MP worlds with large numbers of players (like 30 at a time online per server like Neverwinter Nights did 10 years ago) and modular levels to allow world expansion.
Something like that might be more doable for their limited resources (and overlap into Solo Mod to get enough buyers).
Working out/balancing the material economics, the player Advancement tech/skill trees, NPC strategy behavior for the game --- turning them into game mechanics rules would be alot of work (for the company). Useful if they exposed the scripting logic so that players could Mod them (usually players eventually can do much better than the company does) and better if they offer a 'program interface' to allow real programming to externally drive the game (DLLs or seperate programs to do NPC AI efficiently)
As far as I can tell, the whole idea set could fit into my Humongus Revolutionary MMORPG ideas (my system would be versatile enough to include all of it), but also would be a likely game scenario for a more resonable (and possible) MMORPG.
Now, how they (the company) would be able to avoid the WOW style of running a MMORPG game (where most MMORPGs are these days) is probably the hard part. 2K claims to be 'innovators' but they still create stuff pretty much the same as most other games (just lucked out with Bioshock that had certain theme elements that appealed to many people and could package it easily into the Solo games).
Myself, I think the Player Created aspect would be the way out, but thats really a hard task.