I thought about this a little bit, its pretty much common sense but for those who haven't thought of it.
WARNING DO NOT DO THIS NOW OR WAIT TOO LATE:
Alchemy: most goblins are gonna roll alchemy so stocking up on perfect herbs and other necessary supplies/recipes/etc, stock up on these mats when expansion date is around or start now if prices of these specific items are low or you have time to farm.
Engineering: Same rules as alchemy so stock up on ores and bars for this as well as schematics.
These two are mainly for horde since goblins will obviously have an engineering bonus as well as use alchemy for arenas and general PvP.
While for Alliance the only thing I can think of is LW becoming popular but most worgen that will roll skinners will probably be LW as well, but prices of skins will drop on alliance side during expansion.
Just some general speculation for mats and professions, some professions profits will die down or grow only thing that wont really be affected is inscription( slight demand increase but not much other than that)at least in my point of view.
Don't completely trust me on this speculation. Gimme your opinion, thanks, whatever.