It´s not about farming them now, it´s about the retroactive transmogs, that would be unlocked if a char in your warband did the quest years ago or if you do a Quest now.
A lot of Vanilla quests have rewards that you could not wear because of the armor / weapon class, so they were lost forever as we did either not select them as a reward or did throw them away.
Current quests only show your armor class, not the others.
The warband system was supposed to fix this, by bringing back old transmogs and unlocking all current ones, no matter the class you play. If you did a quest in Vanilla, the rewards would now be added to your transmog collection, which could be a shiny axe your mage unlocked, or a plate armor your priest did.
At the same time, if you do a quest with a cloth class now, leather, mail and plate would also be unlocked on your account.
In beta this was still working and players reported many unlocks, but on live nothing is happening.
That´s why I say, this is not just the bank, it´s much more that is not working and nobody knows if logging in will screw people in the long run, if stuff is enabled again.
Achievements have similar problems, some are reset others are not tracked, it´s as if the warband system is just not rolled out properly / disabled.