You can complete this quest even after the game ended. If your team manages to attack all five bases, but not capture them before the game ends, you can just wait and you'll get this quest done.

I have a 49 twink who is exalted with the League of Arathor, not only do you need exalted But you need level 60. quite lame.

But I've hit revered so its almost done.Actually, if you've hit revered you're technically only halfway through.
Consider the point totals of everything up until revered:

Neutral - 3000
Friendly - 6000
Honored - 12000

Those three combined are the number of reputation points you would have to have earned once you just hit Revered (0/21000). Those three numbers, incidentally, add up to 21000, which is the same as the total number of points the Revered bar requires.
So, not to bum you out or anything, but ""just hit Revered"" only feels like you're almost done, since it's the fourth out of five reputations levels. It's actually only 50% done in terms of points earned/time spent.

EDIT: And that's assuming you only need to just hit Exalted to get the tabard. If you need to reach fully Exalted (999/1000), then it's actually slightly less than half.

I do unfortunately have some bad news, after the release of 5.0 this quest isnt available anymore. I actually find this extremely lame, the reputation has never been nerfed, only harder to be exact... Whats the point REMOVING the tabard?
..

/cries

EDIT: GM have confirmed it is a bug.. the quest will be available again!