A little late, but it seems that Bloodborne will finally receive a multiplayer-orientated covenant that leans towards Jolly Cooperation. Called 'The League', it seems to function similarly to the Sun covenant of the Dark Souls games, where you're to assist other players. What makes it distinctive over regular coop isn't specified, however. In the Dark Souls games you would eventually acquire rewards for ranking up, incentivising you to help your fellow undead beyond the tried & true act of altruism. Unfortunately going by how Bloodborne's handled things as of now, its covenants equivalent yields zero rewards - two of the three are also the exact same thing basically. The arc that leads you to the covenant initiation is primarily only beneficial for the Rune you'd unlock.
There does at least appear to exist a new weapon, called 'The League Cane', though whether that's just a reskinned Threaded Cane is unknown. I assume you'll also get to wear some new digs courtesy of The League leader's outfit maybe?
The Moonlight Sword is a recurring weapon that spans across multiple of From software's games, and is generally regarded as being one of each respective game's best if you're specced for it! I always especially liked its Demon's Souls variant for how light it was; that, and I managed to find it pretty early within the game's lifespan and would occasionally have people asking me where I found out. I never told 'em, though.... In any case, it's set to return in The Old Hunters. Given the strong narrative ties to the moon in Bloodborne's lore, it sounds like this weapon may actually be pretty important from a story context? As is tradition, it'll probably require you to have specced towards Bloodtinge and/or Arcane to wield it if I had to guess.
I'm already sold on the DLC, though this patch may thusly incentivise me to oil the gears before it actually hits. As someone who most certainly prefers to help his fellow man than hinder him (though Bloodborne is the first of these games where I spent a good deal of time invading courtesy of its superb combat), my curiosity is piqued to see how this League covenant works. Plus it's been long enough that I might not be too opposed to giving it a tenth playthrough...