I’d like to share / brainstorm on predictions for the expansion. That way we can prepare for future demand and make some money while doing so.
In general I think there’s going to be an explosion of crafting so I imagine shards, crystals, and clusters will be strong for a while. Also in addition lowbie gear and glamours are likely to experience a spike as well. As for high level gathered items and equipment might experience a drop in price/demand.
Any other thoughts?
Personally I’m going to stock up on shards, crystals, and clusters before the patch.
Here are ideas of 5 players.

Aenemius:
Aside from stocking up on some choice mid-level materials, I’m not touching market speculation with a ten foot pole, honestly.
My reasoning is a lot along yours – crystals/shards/clusters will be useful and valuable for some time, however for the most part the actual materials are harder to guess about. Will philo/myth/soldiery mats be more widely accessible? Will they even be needed for level 51-60 crafting? How easy will the recipes be and will they require any progression beyond the core leveling? I’m simply too cowed by past failure on speculations to make guesses based on what’s available now.
That being said…
We can reasonably assume that a lot of the most-generic things (catalysts, materia, maybe demimateria at a stretch, etc) will be widely required and worth stocking even if it’s just for our own convenience. It’s also worth making the assumption that farming any and all new materials immediately on release will be fairly valuable, even if we don’t make anything ourselves. Recall the Philo mat rush post-launch, and how every single material market has paled in comparison to those, since then, while crafting itself has gotten more profitable as people began to specialize and self-select.
So rather than over-farming and over-stocking on low value items, I’m going to hold off and be ready at the starting line come EA in June, and will probably even put off gearing at 60 – to an extent – in favour of making the most of the initial market rush for any and all valuable materials that appear then.

Fwa
My guess for this thinking would be, there’s very likely to be a fifth tier of materia with 3.0, or sometime thereafter. We already have grade 5 carbonized matter, so it’s honestly only a matter of time.
This being said, people are likely to spiritbond newer items that give grade IV, with a chance at V. Market would be flooded with excess IV materia, with far less people spiritbonding for the lower grades. This is most of the reason why in general grade II materia is currently more expensive than grade III. And why lower grade materia may rise further in price, probably less people spiritbonding getting those materia specifically.
Grade IV will still be sought after for creating current relics (assuming that’ll still be an option) but with a 3.0 relic its likely that the lessening desire for these contrasted against the prospective increased supply will lead to a slow decline in price for grade IV materia.
This is, of course, mostly speculation, but founded in decent logic, I think. And it’s hard to say, with an influx of newer people or any other changes that they have in mind, whether this will pan out or not.

deepdrill
I wouldn’t count on materia playing as big of a role in 3.0.
Yoshi & Co. were really unhappy with crafted gear and materia being too powerful.
I’m expecting materia to be revamped to be similar to jewelry in wow. Possibly also (hopefully) removing the RNG aspect of it.
Moving forward, we will have specializations in gathering and crafting which will make everything more scarce and having a “good” specialization more profitable.

ceeteesalv
The price of level 20ish crafting material is gonna skyrocket.
All the current endgame stuff will drop like a rock as people get past it and find better stuff as quest reward/dungeon drops. However, new people are gonna try to get into crafting, and that would normally mean the price of level 1 crafting shit would rise, but SE was smart and had the first dozen or so levels use censored ingredients. Past that point though, there will be a huge demand from returning players wanting a change off pace, and so the price will reflect that.

Apeman
This would be a good point, but it’s actually the Case that there is price protection all the way into the mid 30s/early 40s due to the beast men tribes for many crafts. All ingots up to Mythril, all cloth up to linen, wood up to oak and some alchemy and Culanarian drops. Additionally, we are getting more beast men in the expansion, which could cover leather.

Can you give me your advice?