The game has very simple mechanics for the equipment and loot: the 11-12 lvl armor is the best in the game, most of the powerful weapons are rifles and machineguns, you can loot as much as you wish.
The main idea is to add some weight to all the things in the game. For example, if you wear light armor and use submachine gun/pistol, you will be much faster than the player with 11-12 lvl full armor and MG-42. Also, the crates, scrap, metal, other weapons and ammunition will also have affect on your mobility and stamina. Your steps will be louder if you have pretty heavy loot too.
This new feature will add more ways to equip your marauder with that kind of things that will help him to be deadly, fast and to carry lots of that precious loot on his back.
It's not very hard to do this feature. All you need is to add 5-8 levels of the mobility and footsteps loudness where 1 is for "very fast and quiet " and 8 is "very slow and loud".
Don't forget that all these debuffs from your heavy loot/gear you would compensate with some kind of exoskeleton which will also may be added in the game. In the same way you would be able to use energetics or chocolate bars to reduce the debuffs.
You know, you will get much more emotions from the raid, where you slowly got to your spaceship with all that expensive loot and didn't die from bots or other players, right?
For the conclusion, this idea will change the balance in the game completely, so in my opinion it has to be added in game after its full release.