There are limits to these enchantments, however, so don't bust out the Mongoose for your max-level character just yet. Although high-level enchantments applied to items equipped by low-level players will have their power scaled down to be more appropriate for that level range, low level enhancements will not scale up beyond their intended level range. In other words, it appears as though the enhancements aren't exactly scalable.
From what can be gathered so far from the patch notes, it appears as though you'll be able to simply enchant your gear as you go. If you use a high-level enchant, it'll be scaled down to you. Players looking for a way to improve their heirloom quality gear now have a method of doing so. Although the patch notes aren't 100% clear on this mechanic, we'll know more once patch 5.4 hits the PTR servers.