To recap what we already know:
The level 60 murloc slaves on the Greengill Coast on the Isle of Quel'Danas have level 70 pickpocketing tables and are in large clusters. This makes them excellent fodder for mass pickpocketing.
My additional trick:
Spam the following macro as you stealth through the murloc packs. This way you don't have to retarget or manually click anything, and it makes the gold harvest much faster:
/console targetNearestDistance 5.000000
/cleartarget
/targetenemy
/script SetAutoLootDefault(1)
/cast pick pocket
/in 1 /script SetAutoLootDefault(0)
/console targetNearestDistance 41.000000
Remove the /script SetAutoLootDefault lines if you already have auto-loot enabled. If you prefer to play without autoloot, those lines will let you auto-loot your pickpocket targets and go back to autolooting off afterwards.
Additional note:
When your server reaches phase 4, there is a quest to set the murloc slaves free. This will no longer be profitable then, so get your gold now!
Update: It's just occurred to me that when people start freeing the murlocs, you'll probably run into significantly fewer "This mob has already been pickpocketed" messages, so it may actually still be viable, especially during low-population hours. Anyway, at least make sure to use it before you set the slaves free yourself.