So when Blizzard announced the method of gaining entry, I was among those who were annoyed. But now, the community managers have stepped in to address the concerns of players like me. The post splits out what Brawler's Guild is and isn't, and probably most important among the "isn't" section is "A major patch feature accessible to everyone (at first)".
And this is where I'm not sure I agree with Blizzard. From a lore perspective, there are definitely bigger things afoot for both the Alliance and the Horde, and there's the addition of the two new factions, their quest hubs, gear and daily quests to look forward to, as well as new scenarios. And that's all great, but for me, Brawler's Guild is the major feature of patch 5.1.