|Don't say we didn't warn you.|
Thanks to the Beta, players are aware that the current crop of Challenge Mode rewards are soon to vanish and become what is now being referred to as 'Legacy' content. To that end, there's a new section in your Achievements window where these things will (presumably) all be placed come the Expansion. Bearing this in mind, it is probably high time to get the Brawler's Guild finished if you wish to do so.
With what was a minimum amount of ceremony for Blizzard, a whole slew of Brawler's Guild achievements changed in Beta, which gives a pretty strong indicator that if you want to do all these achievements at all, you'd probably better knock them off sooner rather than later, because come Draenor, you won't get them using 'current' gear. This makes logical sense of course, especially as these bosses are tuned for current levels of stats and abilities. What is less clear, but I think it might be worth bearing in mind, is that these 'changes' are likely to occur when 6.0 ticks over, which could leave players only a matter of weeks in which to strap on their Brawling Trousers and get on in there. There is also the implication with this that there will be a whole bunch of new Brawler's Bosses to fight come Draenor, which is great news for a 'feature' of Pandaria I'm guessing a few people considered wouldn't be returned to once we left this Expansion.
Needless to say, we've given you plenty of warning. You want something to do over the Summer? Finish this off now :D