A common theme in fantasy novels is that of a lone wizard discovering an entirely aspect of magic and changing the world dramatically, whether for good or evil. Take the Breaking of the World or the cleansing of Saidin in the Wheel of Time, the summoning of the Everstorm in the Stormlight Archives, the creation of allomancy by the emperor in Mistborn, or the Witch of Izaleth's creation of the Chaos Flame or the corruption of Oolacile in Dark Souls.
It would be really cool if when a dwarf with some magical aptitude created an artifact, they had a very,
very rare chance altering some aspect of the magic system. The greater the change, the less likely, but also the more likely it would have adverse effects -- the creation or destruction of a civilization, the modification of a species, the summoning of demons or angels, the modification of geography (if possible), or most likely, the death or stat-elevation of the "artifact's" creator.
Such events could also be caused by gods, multiple demons banding together, or maybe even the death of megabeasts that had achieved a certain number of kills.
I don't know if this is something that could ever be feasible to implement, and if it was, it should only ever happen extremely rarely, but it would be really cool.
Related idea:
http://www.bay12forums.com/smf/index.php?topic=165483.msg7558500#msg7558500