During 2nd event, it was limited to 3. It probably won't (and i hope so) change. Being able to do all professions sounds kind of retarded to me.
It looks like some professions like armorcrafting require 2 gathering skills (butchering and mining) while other requires only one, like outfitter - butchering (as the clothes are directly looted), and which allow you to take for example enchanting (aka runecrafting) as 3rd crafting skill, which does not require anything else as Disenchanting (aka Runebreaking) is included :) 2 in 1 offer !
Well, this being said, do not all rush on butcher-outfitter-runecrafter as it is what i'm going to do and it will be my main way to pay the bills.