You know, i wonder how many people who wish for a multiplayer side of L.A Noire have actually thought about how it would work. Because i don't think having a similar concept like Free Roam in Red Dead Redemption would quite work for this, and if that's what people expect, i believe they should just play RDR.

IF however Rockstar do manage to find yet another brilliant and state-of-the-art way to make a multiplayer game for this, they shouldn't combine it with L.A Noire, but better more just make a different game altogether, or in a sequal because i still don't think it would sit well with L.A Noire.

But i do think it'd be very hard for such a task to begin, i can see it possible making side quests along town of stopping bank robberies and etc. though. But as for multiplayer cases i don't see happening, and i think would yet be an expected feature if multiplayer were to happen.

#9: Skcarkden -

 

the idea for a multiplayer mode mentioned in your third paragraph coupled with my ideas may be what the l.a. noire multiplayer aspect should be like.