The Mephrit Dynasty is apparently part of the Shield of Baal Extermination release. With the last Sheild of Baal campaign book come new Necron Warlord Traits, Relics, and Formations, and we are now seeing leaked images for them.
Definitely check these out, I dont think Necron players will be disappointed.
here is a link to where you can see the leaked images on the Blood of Kittens Facebook page.
https://www.facebook.com/pages/Blood-of-Kittens/281405089788