Backpack in 0.85 may seem like a device which allows you to carry quite a lot of weapons, which you can swap between fairly fast, only penalty is the reload that takes place when changing equipment. Reloading of course doesn't have any effect when you swap grenades and bazookas so in 0.85 you can indeed carry around a lot more firepower than previously.
This isn't how it's going to stay. We still want you to focus on using the weapon you have usable in your equipment and not constantly switch it to something else from your backpack depending on the situation on the battlefield - unless you go improvising and switch between weapons by picking them up on ground quickly with possibility of losing your favored weapon.
The other demand we want to achieve with the inventory system is that you can indeed carry other weapon(s) for the primary purpose of delivering the weapon to stash / somewhere else, as it can be a rare weapon you can't yet use but what you will want to use when you can (related to Invasion mode only), it can be part of an objective (Invasion mode mostly) or you can use it as merchandise.
The design trick is then how to nerf things so that you don't want to carry around lot of different weapons for the purpose of being that Swiss army knife we don't want you to be.
* Slow down motion from carry weight?
* Decrease agility from carry weight, unable to climb, prone, that sort of thing?
* Tilt the kill probabilities against you?
* Slowing down interaction with the backpack by having to watch the soldier do a backpack animation for 10s is definitely effective but .. seriously?
* Make the player want to prefer using the backpack for something more important to carry in battle than lots of different weapons, and when going into "let's get this stuff delivered" state, make the player able to throw out that other stuff to make room for more weapons? Hmm.. ammo? You'd want to have lots of mags (lightweight) for your primary weapon in your backpack when you go to a fight, but when you come back from the fight, you don't have a justification problem throwing away the mags (cheap) to make room for weapons (expensive) and other valued merchandise
* Don't allow putting weapons into backpack, but allow carrying several weapons directly in hands, being unable to shoot with any of them unless all are dropped, making them scattered around a bit? Once again "running with rifles" completely changed the meaning behind those words
You'd trade off ability to shoot with carrying good merchandise, even visibly putting you into carrying mode
And so forth. Suggestions are welcome!