One of the possible delay scenarios I think is a real possibility is Multiplayer's complex faceted challenge building, from some accounts, new modes of competitive game play are being devised in an effort to break from the old.
One thing I'd like to point out is my findings on YouTube with regard to Rockstar's RDR and it's multiplayer set in the old West.
I had already delved into MP for the first time with GTA IV and RDR about the same time before looking at videos, not quite as enjoyable as you know, playing directly yourself, however, one of the earliest uploads showed a much different atmosphere of RDR MP online, less combative, more exploratory and no propensity for 'Griefing' other gamers, for which Rockstar had to institute some penalties into the system, like more instant Wanted levels, however, as you know if you're a RDR die hard, killing someone to be instantly wanted with 5 or 6 kills meant you progressed up the food chain in your leveling faster! haha
I had a hell of a time with spawning, In GTA IV MP I had a hell of a time with some of the kill modes... It seemed like there was good and bad features in particular to each game. I've not had the chance to try Max Payne MP yet, but offer some opinions on how MP can be instituted, or as we learn more, did they get it right so far with GTA 5??