At this point I think it is no longer any doubt that Battle for Azeroth has represented a significant deflation of the value of gold. The gold flowing into the game has been massively decreased through the removal of the gold missions that were ubiqutous in both Legion and WoD.
Indicators of deflation
The major way to tell whether Gold is inflationary or deflationary is to lock at luxury goods. The easiest one by far is TCG pets and mounts as these are limited in number. You can’t make more of them past a certain point so the price should correlate quite well to the total amount of gold available in the game.
As we can see from TUJ the price of a Wooly White Rhino had significant inflation throughout Legion. Since BfA launched the EU price for Rhinos has decreased from about 5 million gold to about 3 million gold.
Ramifications
What does this mean for gold making? Unless Blizzard adds back some gold inflows we can expect the value of very high-end items to remain very flat or to continue falling. It all depends on when we reach the equilibrium for players that are in the process of amassing fortunes.
As players have less gold coming in they will not be prioritizing luxury goods. I expect high-end BoEs, rare mounts and rare pets to either continue to fall or stay stable at their current level.
Identifying the bottom is not something I am comfortable doing as it is notoriously hard to do. Just be aware of the risks if you do decide to enter these markets.
Causes
Deflation is caused by the flow of gold out of the game bien larger than the flow of gold into the game. BfA nerfed one of the largest sources of gold in flow in the mission table and it also introduced the brutosaur as as massive gold sink.
Both of these changes will have contributed to taking a very large amount of gold out of the game, and heavily reducing the in flow.
Looking forward
I expect the current content market to remain steady. This is because this is primarily impacted by players getting gold from world quests and normal play and then spending it on stuff to help them raid, clear M+ etc. Luxury goods may continue to fall however. It all depends on whether the main factor was the new gold sinks or the decrease in gold in flows. If the gold sinks were the biggest factor then I expect the total gold supply to start steadily increasing again.