It seems fairly straight forward to keep armor crafting relevant by making certain pieces of a set craftable-only. So if you want to complete your super duper trooper set, you have to do a certain quest line to get the helm, run a flashpoint to get the boots, get a craftable chest, and so on to complete the set. As long as one piece (or more) per set is only craftable, there would be a market for that piece. And then of course certain pieces and patterns could only be attainable from Ops as well. So some sets would be impossible to complete fully without doing end game content.