There simply isn't a large enough selection of weapons in Fallout 4. Sure, mods make the same weapon feel new and different, but come on, that's not the same thing.
Some Weapons I'd love to see make it into the game:
1) Sniper rifle variations and DMR/Marksman Rifles
2) M21/M14/Mini 14 style rifles/battle rifles (could be modifications of each other, including the Mk14 Mod 0 variation)
3) More SMGs (Bringing back the REAL 10mm SMG would be great, perhaps with the option to be modded into an AR? Speaking of which...)
4) Assault Rifles (AK/M16/MP44 styles)
5) LMGs (The Lewis/Maxim style LMG is cool, but some BAR/M60/Type 99 styles would be Fantastic)
6) Shotguns (A Pump Action shotgun is a must, and more variants overall would be Great, thanks)
7) Lever Action Rifles (I'm partial to my Brush Guns)
8) Grenade Launchers (Really, there's no reason they shouldn't be in the game)
9) More Pistols and Revolvers ( also, true Revolver Rifles [not the pipe guns] would be SWEET)
10) And a greater variety of energy, melee, and unarmed weapons.
A massive Gun Runner's Arsenal style DLC is almost an absolute must at this point, and would greatly add to the game's replayability and longevity. Hell, new armor, outfits, and cosmetic accessories would be great too.
Feel free to add any thoughts on weapons, armor, outfit, or anything else that you think is missing and would love to see make it into the game in a DLC.
Let's make sure Bethesda sees this and acts on it!