Revealed during my Tennocon 2018 art talk. This is just the concept - No ETA or further details on this guy.
I've posted progress sketches of this and other work on my Artstation account if you're interested in checking it out.
Figured I should clarify since some people are posting about this gun being a dual wielding weapon - the only reason it isn't shown like that is because the concept artists only have a few basic stances readily available to us to use: pistol pose and rifle pose. These are purely meant to test the grip to make sure we've designed a gun which can be held by a character. This is also why you don't see the concept artists posting images of tenno holding melee weapons and such. Just a little food for thought!