New Rumour Engine: Likely a Guard or Krieg Officer

That new armored fist teaser is definitely not a Space Marine. The arm is too thin for an Astartes, and the winged skull is actually a specific variant used by the Imperial Guard.

While the official post jokes about Macharius, the technical details, like the internal pistons match the current 40k Cadian and Krieg power fists. It’s likely a new centerpiece character or a command squad refresh for the Astra Militarum.

http://warhammer-community.com/en-gb/articles/fcmvqul0/the-rumour-engine-3rd-of-february/