I've thought that it would be a really cool idea to have these sorts of things doable in an MMO by the players. But the HOW of it always stymied me. No matter how difficult you make the learning of the recipe, or how obscure and rare the ingredients are, the player-base will always grind it out to create as many copies of the same artifact as they can. Sulfuron's Hammer, in WoW is an excellent example. Sure, the first one was a big deal. But it didn't take long before you saw one, or even more, in every single battleground match! And thus does epic fantasy vanish into the nether.
Then, an idea hit me. Rather than hard-coding in the artifacts themselves, let's just code in a framework for how artifacts are created, and let the players fill in the gaps... in a limited manner of course...
This concept revolves around the idea of Inspirations. These would be given out very sparingly, and only to crafters who have reached the pinnacle of their profession, or near to it. I don't quite have the details of that part worked out, but perhaps a fixed number is given when the character becomes a Grand Master, or perhaps they accumulate slowly over time, or maybe they have a small chance of being acquired when a craftsman makes an especially wondrous creation.
Then, these Inspirations can be used on the corpse of a named or otherwise very special creature. Or maybe even on an ultra-rare resource. When used, the crafter is given a pseudo-random special item type (Blood of, Tears of, Essence of, etc) that is tied to the creature/object it was acquired from. This special item will be flagged with attributes based on the skills, special abilities and such of its parent object.
The crafting interface would then allow this special, artifact-resource to be added to any regular creation. So if they player wanted to make an Artifact-quality chair, they could. More likely they would use to it imbue armor and weapons, though I could also see extending its uses to larger constructions such as buildings and ships!
For example, suppose a player used an Inspiration on Gorgofen, the infamous Black Dragon whose spittle could eat through even the toughest armor. They receive a special ingredient, called Essence of Gorgofen. This essence would take some of the attributes from Gorgofen (dragon, acid-breath, etc). Then, when the player adds this special essence to something they are crafting, that item will be appropriately imbued with these traits (this is the framework), flagged as an artifact and the player would have a chance to name it.
This system allows players to create unique artifacts in a meaningful way. They get to choose how, when and why to use their Inspirations, and then they get to choose how, when and why to incorporate those inspirations into a fabulous, one-of-a-kind creation that will be written about in the history books!