The Gun Runners' Arsenal along with the Courier's Stash is being release on the 27th of September, a week after Lonesome Road. It is confirmed by Jason Bergman that there will be 27 new weapons and 40 new mods.
In one of the pictures, we can see a unique Fat Man, "Esther". Considering the fact that Mini-Nukes are really scarce throughout the Mojave Wasteland, indeed there are only 14 or 12 with the Wild Wasteland trait, the unique Fat-Man would be utterly useless, unless the mini nukes are sold by merchants.
J.E. Sawyer said on his Formsprings that there will be a unique variant for some weapons that don't have any, like the Assault carbine and a common variant of unique weapons like That Gun or This Machine. In fact, in the game's file, as well as the G.E.C.K, This Machine is referred as "WeapNVBattleRifleUnique" meaning that the cut "Battle Rifle" which might be the M1A1 Carbine or the M1941 Johnson Rifle, the latter would be more likely as it "competed unsuccessfully with the U.S M1 Rifle", which was the source of inspiration of This Machine, will appear in the Gun Runners' Arsenal pack.
Thank you for reading.
:)