If i need some quick gold i do Bastion of Twilight 25 heroic trash farmruns with my druids. Clearing the first room - reset all instances - and again. Selling everything at the Vendor (no Lockboxes) gives you ~800g per char per 10 runs in under 15 min. Before entering the Bastion leave the grp, so every char gets his own instance and loot - activate Broadcast all - run in the middle of the first room - spam aoe - use Findle´s LootArang - turn arround and run out.... its like multiboxing Diablo 3

Not sure if its worth with 3 chars or if Fireland trash run makes more sense.

For all Garrison Gold making you need a decent amount of time to keep it running properly. BUT i think it could be worth it pushing your Followers and Garrison up and make some easy Gold in Legion.
All you need is a Tavern/Inn(lvl3) and Trading post(lvl1). Recruit Treasure Hunter every week ... once Legion comes out, Treasur Hunters will give you garrison resources instead of Gold. So you will cap your garrison resources pretty fast. Now you need the Trading Post, go to the vendor and buy the sack of Gold. For 10K Resources you will earn 3K Gold.
It realy depends on how blizz will change the sack of gold or the droprate of resource missions with Legion.... we will see