I think there are plenty of guns without customization. The loadouts alone practically let you do that by choosing your gun, which are similar-yet-different enough that each grouping (primaries) could be considered one gun with different traits.
Which is honestly a big reason I don't like COD, because all their guns are seriously the same, customized or not, and sorely underbalanced. But I digress.
I hope that never makes it into this series though. I miss some of the different guns. The old shotgun (ya know, from when it took skill to one-shot anyone), the mauler, sentinel beam, flamethrower... the guns they chose are great and all but I liked the diversity and with the balance they seem pretty capable of, they seem like weapons that really should have been included.
"The point of war is not to die for your country. It's to make the enemy die for his."