The variety of weapons and customization are great, however there are some things I'd like to see added.
A .300 Blackout SBR similar to the honey badger would be really cool. What would make the weapon unique is the noise reduction with very high handling stats. The downsides of the rifle could be range and accuracy. The cartridge was originally designed for SOCOM but did not last very long, however it is quite common among civilians.
An alternative to the above would be the Colt Mk 18 Mod 0. These are basically short barreled M4s that are oftenly supressed and used by special forces.
My second request would be the ability to only carry 2 weapons in solo/co-op in exchange for a few extra magazines or faster running.
My third request is the ability to remove the backpack in exchange for, again, faster movement but also reducing the amount of equipment/ammo carried.