Please remember that this is a rumor and to add in the appropriate salt.
According to other rumors, we are looking at Orks sometime this summer around or after June.
via Adeptus Astartes Facebook
Via industry insider
“Look for the return of Abaddon and his entourage this year on the heels of the Orks.”
A little follow up from another source from Bolter and Chainsword who has had rumored releases before.
I think the Abaddon model was in the works over a year ago, so it's just a case of ideal release date.