Before I begin, I'll admit that this is fairly unlikely, but hear it out anyway and make your own choice.
Zombies is making its last map for a year and a half, so want to end with a bang. The map is confirmed to be epic sized with multiple areas and lots of cool things and whatnot, whats more epic than nearly doubling the number of weapons?
Big maps = more wall guns to fill it. More guns? WaW weapons.
This is coming out with the first chance (for many players) to use WaW guns, so maybe they're linking the maps by using some WaW guns.
The trailer only showed weapons available in the WaW maps box (M16, 74u and ray gun) and of course and olympia, which is the replacement for a double barreled because of their similarities. (same would apply for stakeout and trench gun, m14 and geweher, and more)
A flamethrower is in the trailer, assuming the perk isn't attachment giving, this means either the flamethrower is back, or they're adding an Ak47 or Enfield upgradable to have an under barrel flamethrower.
let me know what you think ^.^