Future speculations and/or predictions?
Mystic Coins became more expensive because they became harder to get naturally, yet are still a requirement in the same quantity. It’s a supply:demand thing, not a speculation thing, for the majority of its price increase.
Anyways, you should definitely keep your T6 materials, as they’re likely to go up in price. This is a given thing, as they’re not going to be any more easily obtained than they are now, yet will be needed for a large number of new things. The only relevant “speculation” part of this would be that Powerful Venom Sacs are going to go up. They’re not used in a Legendary weapon, and play into being put into a Legendary weapon the most. On top of that, ANet have started flooding the market with them in much higher quantities than the others, leading to a question of “Why?” when there isn’t a reason for it now.
Other fun predictions would be that Ambrite is going to become more expensive due to them putting in stuff that cares about it, Piles of Putrid Essence is going to go up due to it being less common (we’re away from the undead, yo), Giant Eyes are going to start zig-zagging in price heavily (and trend downwards in the extreme long haul), Charged Lodestones will go down (because ANet hinted at it), and all of the region specific Chef stuffs will start to trend upwards (as will a couple of other food items, though not in a relevant amount). Oh, and they’ll do something to make leather not a completely worthless material, but then cause people to cry out and compare it to Damask.
There are plenty of other fun predictions to make, though quite a few of the others would probably have no where near the profit potential/safety as the others (such as Nopale getting love).
This is gonna be almost impossible for me to prep for, I am so excited, when I try to think about what I know vs what to prep for… all of a sudden I can’t think (sobs)