Saw another screenie of the rifle decked out in camo from the Japanese convention vids. It clearly is in the AR family judging by the front sight. I'm still sayin it's a modded assault carbine where the stock mod includes the magpul like buttstock, the picatinny rails and the paint job. I really doubt this is a distinct weapon in it's own right. 3 AR family weapons seems just a bit too much to me.
Someone on NMA suggested it looks a lot like the K-YOTE Varmint rifle.
http://www.mgarmsinc.com/k-yote.html
It really is a spitting image of the gun in many ways, from the stock to the rails and even the camouflage. However, we've seen the varmint rifle and it doesn't look like that.
Also, the K-YOTE looks a bit longer than the gun in the game, which appears to be equal in length to the Assault Carbine, suggesting it's a mod or unique version of that gun. And the stock, like you said, could just as easily be identified as a Magpul Precision Stock.
Still, it's interesting that the gun is so similar in many ways.
I'm thinking the Camoflage Rifle is a unique. It could be a Carbine with 3 mods, being camo, scope, and stock. The rails could show up with the scope mod, but why? There's nothing on them, as far as I can tell. So it makes more sense that the rifle just started that way.