With the 90 boosts we want to ensure getting professions to a point where they're usable by your character supports where you want to be in the game, and doesn't require things like going back to low level zones to farm materials for crafting. Of course if your character is above level 60 when you boost you get the bonus of fully leveled primary professions
. If you aren't 60 when you boost, we want to ensure professions are fairly painless to get up to a level where they're useful for your newly boosted 90 (or even if you just never bothered leveling them before). In Warlords, Herbalism and Mining will be changing to a fishing-like structure, where skill ups can be obtained from any nodes, and only the result of what you get is based on skill level. Materials to level up crafting can be obtained wholly within the newest content (Warlords) with catch up recipes like Cooking saw in Mists, and potentially additional paths to allow players to avoid having to go back to old content, if they wish.
From the Warlords of Draenor Alpha patch notes
Herbalists can now harvest herbs throughout the game world without hard skill requirements. The yield an Herbalist will be able to harvest from each node is now determined by skill level.Miners can now harvest mineral nodes in outdoor areas of the game world without hard skill requirements. The yield a Miner will be able to harvest from each node is now determined by skill level.