I have seen a possibly fake screen shot of someone getting a shoulder enchant onto shoulders. Which I am assuming; if it is a real screenshot, the enchant was applied using some sort of trade window exploit. Which I have heard of but am unaware of how exactly it works. Can't find very much info online either. Also, I don't suggest exploiting due to the risk involved. You will lose the enchant eventually, and you will face some sort of punishment. Which may be light or may be a perma ban. Reward is not worth the risk.
Naxx enchants have always been able to be applied to BoE items. Every enchant works differently in classic. They became more uniform from BC forward. Naxx enchants were a major commodity in Classic and into BC due to the fact they would be phased out of the game after Naxx. Expect to see them later in classic, and expect them to cost A LOT.