People will probably hate me for even suggesting this, but I think ammunition should have weight in this game. It was nice being able to carry around 20,000 rounds for a weapons in FO3, but it also made things both unrealistic, and a tad boring because I never had a moment when I had to make a tactical decision as to what gun to use (i.e.- this gun has much lighter ammo than that gun so I can carry more of it). Additionally, since it was nearly impossible to run out if you carried all your ammo on you, there was never a need to switch weapons in combat or worry about running out or making every shot count. I think that by forcing decisions like that on the player, it will make for more interesting and more significant prioritizing of weapon use in game. (Generally stronger ammunition weighs more for guns, and I imagine a microfusion cell probably isn't all that light itself.) Obviously, this should be done carefully since the game doesn't fall into the category of survival horror precisely (and somewhat ironically), so the player shouldn't ALWAYS have to rely on some kind of melee weapon.