Basically, Gun Emporium is a section the combat arms tabs that: as said in the video, allows you to combine two weapons of your choice to create one "Super weapon." Balance, however, will be kept somehow. I think it'll be like this:
Let's say you have an AK-47 and a G36E. You want to fuse the two together to get an uber awesome weapon of ultimate pwnage, an weapon that's super strong, high fire rate, good portability, scope of death, etc. Well, they'll balance it out. tHey'll increase damage, but not so much it R@
pes other weapons, maybe a 3 shot kill or 2 if lucky. The Rae of fire will be like the ACR, SCAR-L, or maybe a slightly faster AK-47. The portability will be that of the G36E or a bit less. Recoil will be a bitch, since recoil is bad for all of them. Scope will be built in.
Bascially, it'll be a bit better than almost any non-fused weapon, but it won't be THE super weapon to end all weapons. It'll stay somewhat balanced or a bit better compared to all other normal weapons, but equal or a bit tweaked form other fused weapons