The following is an assortment of facts we can be reasonably certain of as well as my own speculations, conclusions and expectations that I've been taking into account while preparing for patch 4.3.
Potion materials requirements are being greatly reduced. Most cataclysm potions will take just a single herb and a vial to make. Expect potion prices to drop significantly and once players get used to new low prices they should start selling in greater numbers too.
Epic gem transmutes. We don't know what the materials costs will be and we don't know how the cooldowns will work either. We don't even know for sure if they'll be in the patch though it seems very likely. Blizzard hasn't said a thing about transmutes but from what they have said about the availability of epic gems don't except an instant gold mine. Transmutes will likely be limited by both high materials costs and long and/or shared cooldowns.
Rare gems. Expect demand for rare gems, especially inferno rubies, to skyrocket. Prices will go way up too and for the better cuts (again especially infernos) should stay up for months.
Pyrite and Truegold. None of the new patterns use truegold... Unless Blizzard pulls a fast one and changes a bunch of recipes to use truegold instead of Hardened Elementium at the last minute. We probably aren't going to get epic gems from prospecting pyrite either. Prices for both truegold and pyrite are already down, expect them to remain low. The good news is prices probably won't drop any lower than they are now and may even go back up somewhat due to prospecting pyrite for rare gems.
Chaos Orbs will be BoE. Expect prices to rise initially with multiple players continually barking trade trying to corner the market on them. Demand should be high enough to hold prices relatively high for at least a few months but eventually they'll drop way down as has happened with all other "orbs" that have become BoE in the past.
It's possible they'll make Dreamcloth BoE too. Don't count on it but don't be surprised if they do either. If dreamcloth does become BoE, expect prices to follow the same pattern as chaos orbs.
Maelstrom Shatter. Enchanters will be able to shatter maelstrom crystals into 2 heavenly shards. Expect the price of heavenly shards to go way down initially and then rather quickly go back up. Maelstroms should steadily increase in price. Eventually they'll stabilize with crystals going for roughly twice as much as shards. I expect prices will eventually settle down around 75g per shard and 150g per crystal.
New gear means greatly increased demand for gear enhancements. Spellthreads, leg armors, enchants, belt buckles, gems will all see much higher demand and higher prices will follow.
Naturally with higher demand for so many different crafted goods, demand and prices for common cataclysm materials will rise too. Prices of cataclysm herbs, ore, bars, gems, enchanting materials, leather, hides, volatiles and so on should all rise.
Update: According to wowhead PTR data it seems the new patterns do take truegold now after all. I figured they might do that all along. Now I gotta wonder when the change was made and unless it just happened today how'd I miss it? Thanks to Itzal for pointing this out.