If they allow anyone to boost a profession for any character, then I totally agree that the crafting market will be decimated. There is a thriving market for old school mats which in turn keep the cost of mats at reasonable levels. If you take away the market, the mats costs will skyrocket because not everyone can afford or want to purchase a boost. Thus completes the financial circle for Blizzard as it will eventually force all to buy a boost due to either the cost of I game mats or he scarcity of them.
this isn't buy to win, but it's skirting very close to the edge as it's effect will be to force people to feel the need to buy a boost unless they are happy to farm very old content in order to get the required mats