Here are the biggest changes:
- Profession-based bonuses are gone. And, though we may be losing some perks, with the stat squish and resultant rebalancing in Warlords, this is the ideal time for Blizzard to make this switch. The end result is that you won't have to pick a profession for a specific combat bonus... but can have whichever professions you most want.
- You can gather anything in Draenor, regardless of skill level. We saw this happen with mining and herbalism in Pandaria in patch 5.3, and now it's expanded to cover all gathering professions, making it easier to level up a gathering profession from zero. Players with higher skill levels will gather more materials than players with lower skill levels.
- In addition to gathering professions being easier to level, crafting professions all have catch-up recipes that will let you level from zero onward using Draenor materials. This will probably make it more expensive if you plan on buying materials (since everyone will be looking for the same new-world materials), but less of a nuisance if you're gathering your own.
- Garrison buildings will allow you limited access to professions you don't have... or improve your abilities in professions you do have.