Inventory charging would certainly be welcome. I'm managing as is, instaswapping my empty laser rifle to offhand, then wielding my backup from my inventory, and swapping back and forth as needed until I've thinned out the monster spawns enough to equip my Cleaver again.
I do lose a turn equipping from inventory, since nothing I have is a quickkeyed item, but I'd be doing that anyway with inventory recharging, since I'd simply wield the backup and send the empty rifle to my inventory to charge. However, I wouldn't have to bother with the extra action of swapping the Cleaver, nor would I miss the utility of instant melee kills it provides during the time I'm charging my empty rifle.
I do agree that everything should recharge equally - offhand doesn't seem to me to be any more valid then inventory as far as that is concerned, and if balance is the issue, offhand recharging still provides me with infinite ammo between MAc and N1 modded weapons. It just isn't quite as convenient as it could be =P
And yes, floor recharging isn't worth the trouble, either from a coding perspective or a gameplay perspective. If we were going out of our way to make it as realistic as possible, sure, but then we'd also have to make AoHu the default game mode ;)