Investing for future changes to the game is something that can be very profitable in WoW, but it’s also very high risk. Phase 5 is getting closer, and will arrive in a month.
A look at Phase 4
To get a good idea of how the price of an item that will be needed in Phase 5 might behave i we can look at items for Phase 4. Mooncloth was a target before Phase 4, as casters would need significant numbers of Mooncloth for their Bloodvine sets. If we look at pricing data from the Undermine journal, we can see that the price started rising around the end of February. It rose quickly for two weeks, and then it sustained at a decent price. Then as soon as ZG opened the quantity ballooned like crazy and the price fell signfiicantly. This indicates that players stocked it heavily and dumped it all at the same time.
P5 items so far
I’ve bought some P5 items for my own use, mostly nature resistance gear for raiding. All of these have significantly increased in value. This will continue for a while. NR gear will however not be useful at all after you can clear Huhuran, and players will get NR gear from AQ to replace pieces as well. These kinds of items are unlikely to keep value after phase 5 launch.
Valid until phase 6
The best items to invest in would be something that you need more of in both phase 5 and phase 6 than now. Obvious candidates include Black Lotus and Arcanite Bars. With Titanic Leggings coming in p5 Arcanite could go up, long term it will also be needed for naxx attunement for players that are not exalted with AD. Flask usage will likely increase in harder content assuming AQ and Naxx are more difficult than Blackwing Lair has been. Other examples include items needed in consumables that come in p5 like the weapon oils and elixirs of greater Firepower that mages will use for the rest of classic.
Is it too late for P5?
I’m assuming that it will not be yet, but time is short. Likely any launch date announcement will cause a large spike like Phase 4 caused. For items that do not keep their value after phase 5 you will want to sell around phase 5 launch or within the first week before the gates open. This should be the peak price range as players panic to get ready, and the hoarders have not dumped their stock yet.
Should you invest?
Honestly it is extremely risky. If you sell too late you can end up not profiting at all, or even losing gold. Predicting the future is incredibly hard. Personally I would only advocate getting what you need or items you have very strong analysis to support. Keep in mind there will likely be significant differences between realms as well. I will not advocate for any markets, and I have personally not invested at all, outside of a single Hammer of the Northern wind.
Anything that is out in public, like this blog post will likely be done by a significant number of players, which will drive down profits. If you want to do this you have to make your own analysis. Look at recipes that are coming in particular, as well as consumable lists that may change, this is the main source of new value.