There are some really good videos and informational tidbits that are out there about the new XPAC dropping 8/30/16. I will list a few URLs here. If you find more that have good information, list the URL in a response to this post. Thanks!
https://youtu.be/tKbpc-SHxiE Legion Artifact Introduction
https://youtu.be/FmTahZ60C0U Legion Artifact System Preview. How the artifact system affects your character.
https://youtu.be/_6u4OKWgAgs Legion Artifact Weapons and You.
https://www.youtube.com/watch?v=OMQTsPd1tig Legion: New and Returning Players' Guide - A Complete Overview.