The reason it is repeatable is because if your not a NE then you can do this quest over and over and over and over and over and over (you get the idea) again to get exalted status with Darnassus so you can get a sabre. There ya go!

Based on drop rates and reagents needed..

for Revered to Exalted you need 21000 rep
21000 / 75 = 280 turn-ins
280 turn-ins = 2800 Morrowgrain

Morrowgrain drops approx 37.9% of the time according to wowhead stats, but drops 1 - 5 morrowgrain each time it does.
at 2.5 morrowgrain per drop, 37.9% of the time - you will need roughly 425 Evergreen Herb Casings.

Casings are made from 2x Un'Goro Soil and 1x Packet of Tharlendris Seeds, so this means 850 soil and 425 seeds.
The seeds are sold by a vendor in Darnassus for 10s each (is this affected by rep?) therefore the seeds will cost you 42.5g

Un'Goro Soil drops most in Un'Goro Crater from the Gorishi bug things, roughly 1/3 of the time, maybe a bit more. This means you will need to kill around 2500 of these mobs to get your soil, assuming you don't pick any soil up from the ground. If anyone can estimate how long you'd be killing mobs to get that done and how often you'd come across a pile of soil that'd be wonderful.

Last on the list is the 10 minute cooldown on cultivate seeds, this means that once you have spent your 42.5g to buy packets of seeds, and killed your 2500 Gorishi mobs to collect 850 bits of soil, you need to spend 70 hours and 50 minutes cultivating them. I suggest you do it while you grind tbh.