[member="Veiere Arenais"]
Well, I've been playing WoW since release and have participated in pretty much all aspects of the game at one point or another. (Lead a hardcore progression vanilla guild, hardcore PVP, and now casual stuff.) WoW has been a major influence in my life, for both good and bad reasons.
The pay-for-subscriptions-with-gold option came into being sometime in WoD. Blizzard introduced the WoW Token. You can purchase the Token for $20 USD and then sell it on the AH for a price that's determined per region. The gold price fluctuates based on supply and demand. The buyer of the Token can then use it to redeem for a month of WoW. What this does is that it encourages players to "buy" gold from Blizzard instead of going to third-party websites, which are full of risks. (You purchase the WoW Token with Real Money, list it on the AH, and get gold in return.) Currently, the NA WoW Token averages around 44,000 gold. I'm not sure how it's doing on the Europe region.
Gold has been fairly easy to earn in WoD. The Garrison has missions that return gold and you can equip your followers with the gold-increase trait. If you have an army of alts with properly equipped followers, you can make a significant amount of gold by just logging in every day. Plus, the Jewelcrafting profession building has a daily (if you place a follower there) that returns about 250 gold per day. It's not unusual for me to earn about 3000 gold a day by just logging in for 30 minutes. If you include the (rare) missions that return over 4000 gold and the other auctionable items, then the rate of income increases significantly.
Blizzard is nerfing the Garrison in the pre-Legion patch, so if you want to utilize its gold-earning functionalities, you best start now. Also, they're removing the ability to turn in Garrison Resources for gold (via the Trading Post) in the same patch, so don't forget to burn through all of your excess Garrison Resources.