It would make no sense to me if they do end up doing this, since so many crafts are dependent on other crafts. For example, as an archer who loves to make her own arrows, I have to utilize carpentry, goldsmithing, blacksmithing, weaving, and alchemy. Making any gear involves not just, say, weaving, but leatherworking and armorcraft as well. For this reason I doubt you'll be limited to doing just one craft, but I can see SE added some sort game material that will allow you to only "master" one (or a limited number) of crafts, as Griss says. Personally, I think this would add much more value to what a person selects to "master", whatever that may end up meaning. I hope it ends up being something like getting a relic in FFXI.