I agree that adding a new mode would take alot of time and resources but I just don't think they (Obsidian) should be allowed to get away with adding such a horrible mode and expecting us to just put up with it.
I don't like companies taking my money, giving me a crap excuse for a mode and then trying to fob it off with weak excuses.
I'll stop ranting now because I'm going off topic.
Keep in mind though that with the way the multiplayer aspect is at the moment, this game won't servive a month online due to returns and trade ins, so with less people able to buy DLC, how long will DLC support last if no one is buying it?
If the online is fixed, then people will keep the game as something different to play online and henceforth they have a larger market to target for DLC.
Just my opinion mind, so I could be wrong about everything.