One of things that most of the people did not like about the Lumia 950 and 950 XL is the Plastic build. Most of us would like to have a Windows 10 Mobile which comes with build like the Lumia 930 and 925 and seems Microsoft is planning something similar with Lumia 850.
OnLeaks has posted a quick video of the alleged Lumia 850, which shows metallic rim all around with curved edges, removable rear, and with 3.5 mm audio jack placed at the bottom. The phone also has camera hump which is very similar to Lumia 640 XL along with Microsoft Logo at the end. This logo design pattern is similar to what we have seen on the recently announced flagship devices.
— OnLeaks (@OnLeaks) December 4, 2015
Notice in the video above that there is no dedicated camera button, and the volume knockers are similar to what has been used on most of the Lumias. That said, if the alleged pictures are actually true, Microsoft is yet to make drastic shift in their design pattern. So take it as pinch of salt right now.
Update: Adding to this, @evleaks mentioned that Lumia 850 is code named Honjo and comes with gold coloured trim and a golden Microsoft Logo. He also claims that the phone as a front facing flash.
.@OnLeaks In real, non-CAD life, Honjo has gold-colored trim and a golden Microsoft logo on the back (as well as a front-facing flash).
— Evan Blass (@evleaks) December 4, 2015