REWRITING THE STORY
Say for instance, that round one is a Kane-&-Lynch-style gang vs gang heist objective. Round two involves the thieving team having to protect its highest scoring member from the murderous wounded pride of the opposition. A Capture The Flag win leads to a dynamically-generated Protect The Leader challenge - the whole experience (in theory) effortlessly blending the traditionally irreconcilable joys of the scripted and the emergent.
The factions will be the same encountered in Max's single-player saga, and the scenarios played out will detail their unexplored stories, set both before and after the solo game. See Max Payne 3's multiplayer as operating in the same way an ongoing TV series fleshes out the main story thread by doing a spin-off arc based on a supporting character. It's an exciting idea, and could break down the barrier between game modes, demolishing the traditional idea of a 'story mode' by turning both single and multiplayer into differently-shaped parts of the same narrative.
But there's much earlier precedent for this sort of thing within Rockstar's work. The studio might only be officially starting in this direction, but Red Dead Redemption was clearly an early sketch for it. The architecture of RDR's online mode was all about the dissolution of single-player/multiplayer boundaries. Its use of the main game's open-world map as a canvas on which to smudge together organic exploration, dynamic play and more traditional MP skirmishes was an inspired move, and one that's becoming a more obviously important evolutionary step for gaming.
The thing is, ever-escalating development costs - plus the starkly polarised thrive or dive nature of sales - mean that triple-A games need to change shape or die. For evidence of the seriousness of the situation, you only need look at the number of devs who have gone under this generation, and cross-reference those statistics with the increasing ferocity of the industry's (not always well-directed) war against piracy and second-hand sales.
Big budget games now need to be more than games. They need to be platforms and services that continue to be ongoing parts of players' lifestyles long after the initial launch window hype. Put simply, publishers need to keep their discs on your shelf, not Gamestation's Pre-Owned rack. That's why Mass Effect 3 added multiplayer, and that's why it encouraged online play by tying the mechanics of that multiplayer to success in the main campaign. That's also why it hit players with a fully connected multimedia assault, using iOS apps to fuel their obsession with the game-world and enabling them to further shape their story even when not playing - we doubt your GTA V experience will be limited to one platform.