The Brawler's Guild
is included in patch 5.1, but the invitations will probably not be available on the black market auction house for 24 hours. It is unclear if the NPCs who drop them will start dropping right away or if the drops will be delayed as well. Nethaera has the details.
With the latest patch, 5.1 "Landfall", we've introduced the new feature, the Brawler's Guild. As we previously announced, entry into the Brawler's Guild is by invitation only. Invitations can be found on the black market auction house, by invitation from somebody within the guild, and occasionally as drops from certain Horde and Alliance NPCs. Before you rush to your realm's black market auction house, we wanted to make you aware that invitations may not be available immediately upon realms going live, but should be showing up within the next 24 hours. We wish those of you who choose to take on this next challenge the best of luck in your endeavor.
To paraphrase @BlizzardCS
, don't make a mad dash to the BMAH today. However, they do say "may", which could mean that invites will be available before tomorrow. No need to camp, though. The number of invitations is only limited to those who can afford them
Will you be fighting in the Brawler's Guild? Or don't you want to talk about it?