All permanent item enhancements provided by Enchanting, Engineering, Leatherworking, Tailoring, and various vendors and quests are now able to be applied to items of any level. This means all enchantments can now be applied to heirloom items.
High level enhancements applied to items equipped by low level players have their power scaled down to be similar to enhancements intended for that level range.
Low level enhancements applied to items equipped by high level players do not grow further in power beyond their intended level range.
Anyone who makes gold off enchanting is probably going to freak out when they read that.
Then again it could open a bigger market for various cool enchants from all expansions for any player below that expansions level cap.