Perhaps the interface could be changed to an extensible form, like the fields next to the toolbar where you can toggle ALT-view, night vision, exoskeleton etc.? Mods that introduce new weapons could then add slots as needed -- it wouldn't change anything for people playing the vanilla game, but it would be very convenient for people who use mods.
I can think of two arguments against additional slots. Let me refute these before anybody else can bring them up:
- If you want to play with a new weapon, just substitute it for another one that occupies the slot.
Experience shows that people are lazy. If switching weapons means you have to take one weapon from your inventory, insert it into the slot, and put the other weapon back into the inventory, then it is too much work and it is likely that you will replace the one weapon for good, never touching it again in your game. It's so much easier to just use a hot key to switch weapons -- and should you ever run out of hotkeys, there's a good chance you have too many mods installed anyway.
- It is not realistic that one little engineer could carry lots of weapons plus the necessary ammo!
Well, that one little engineer has no trouble at all to fit entire trains, complete with locomotives and wagons, right next to tons of rails, several chemical refineries, assembling machines etc. into his pockets! So why shouldn't he be able to carry a few more weapons?