Obliterum is made by destroying crafted items, so for money making purposes obliterum is pretty bad. The prices of obliterum might be higher for a moment, when only handful of people have the quest chain done, after that when more people get the forge the competition drags the obliterums price down to what is sum of the crafted items cost in AH.
So you wont be making any profit buying items and destroying them into obliterum. Only way to make money is if you gather resources yourself, and craft the items yourself.
Also, double gathering is pretty bad since you are gonna get lots of blood of sargeras without any way to use them except when upgrading items with obliterum. Double crafters are in the worst situation, they are left with more niche ways of acquiring blood of sargeras since BoS is mostly gathered resource.