Goldmaking is a fun way to play the game, but in general it is not in Blizzards interest to make any profession or flipping method too profitable.
What makes things profitable?
To understand this point we first have to look at what characteristics makes something profitable, and in particular what makes something very profitable. For a high profit margin item it needs to be hard to obtain in some way. If it’s a crafted item this usually means either a BoP crafting material, or a recipe which requires a lot of effort to get. In addition to this you need demand, so the item needs to be useful. Either because it is powerful, useful or cool. Some examples here is the vial of the sands recipe which used to be incredibly rare, which lead to incredible profit margins. On the other side items like expulsom or primal nether in TBC limits access to crafting the finished items. This was why the catch up gear was so profitable in BfA and why the AH wasnt flooded with spellstrike gear in TBC.
The best demand is always for power-increasing items, which have significantly more demand than anything else. WoW is for most players a game where improving their character is a main gameplay goal.
The legendaries case study
One way we can see that Blizzard wants to limit profitability is the evolution of the legendary market. At launch the required investment was incredible (I spent 30 million just on leather), leading to very high profit margins as the barrier to entry was incredible. In 9.1 the barrier to entry to craft rank 6s was much smaller. You just needed to do the campaign, in addition to already leveling much cheaper legendaries. Now there was one barrier, that kept prices high. Korthite Crystals could not be target farmed and represented a very significant bottle neck.
Now in 9.2 Progenitor Essentia can be farmed indefinitely, and once again the barrier for getting the recipe is quite low. And Rank 7 legendaries very quickly fell to the lowest price level a max rank legendary has ever had this expansion. This is likely a conscious choice by Blizzard, as expensive legendaries have been a consistent pain point for loads of players.
No more demand bottle necks
The other thing Blizzard did with 9.1.5 was to remove the weekly reset of soul ash and cinders. Before you could get these once a week, leading to insane demand on the reset day. Concentrating demand will increase profits on those days, this happens regularly with consumables and anything else that revolves around the weekly reset. With all currencies for legendaries now being freely farmable the margins are more even across the week and there is much less of the short term demand spikes leading to price hikes.
Expensive power is bad for casuals
Too expensive power increases is probably bad for Blizzard. On some level it will of course drive token sales for real money, but if players can get two legendaries, a mount and some consumables for a token, that is a much better deal than just getting one legendary. Particularly with a system as central as legendaries having them be too expensive will make it feel like you are partially locked out of the game.
Long term profitability
In markets where the barrier to entry no longer matters my experience is that profit margins typically settle in the 20-30% range. This is still quite good, but you can’t expect significantly higher profit margins outside of making good investment decisions before material supply rises or Blizzard chooses to add hard to get recipes or BoP materials.
I expect to see Blizzard keep most power increasing items limited in demand like the unique-equipped aspect of 262 gear, and with a low barrier to entry. It is not in the games overall interest to design professions around maximizing the profit players with a profession can earn by trading with other players.
Hopefully though they will design professions around the expectation that player trading is valuable. Progenitor enhancements are a great example here with all of the optional reagents freely tradeable, giving strong incentive to more professions than before. I hope they increase interconnectedness and let every profession have recipes and items that are useful to other players and at least semi valuable. In Shadowlands certain professions have been left in the absolute dust. Just compare the price of a shadowlands enchant to the price of any of the ilvl 262 pieces.