But every new character made that wants to craft old expansion stuff will have to level using expansion specific materials. Stocking up on profession materials that are already high in demand can be a great idea. This will primarily be materials used to craft the various mounts. Ghost Iron, Trillium, Living Steel, Pyrium etc. are all great candidates to stock up on.
All of my gold came from everyone buying stuff at a really marked up price for instance BS 2h mace if it proced epic i was making at least 125k per one and i was making batchs of 10 to 15 it was like 25k for blue and 125k+ for epics at the time. And i was buying the ore for like 16g to 40g a pop so huge profit. Im still trying to figure out what im gunna do now to rebuild it will be a slow process now.
I think that's server dependant. I make a lot of Golems, but the price on my server is high enough that you could buy all the living steel and still make about 20K (almost 200kg on AH). Its just that you proc all the way up the chain. You proc 20% of your trillium, and then 20% of your living steel. SoH and Ghost Iron are such low effort farms, too. 20% of 180 Trillium Bars at 500g is 18k more profit, 20% of 150 Living Steel at 3500g is another 105kg. That's an extra 25k profit per Golem. If they stop selling stockpile them for the next expansion, they always boom with the price of herbs. And a consistent 20% proc rate is the opposite of RNG, its extra free stuff as a benefit to completing an extra quest (not to mention for new alchemists the investment of leveling Vanilla Alchemy). You're looking for some get rich quick scheme, where the real way to build wealth is patience and volume. No market is going to be viable because you want it to be. Only because you make it viable.