It has a system like that for souls already: All of the Soul of XXX items you grab can be hoarded and used when you need them, without the risk of ever losing them.Probably never gonna happen, but game would of been a lot more enjoyable and less of a grind if souls were separated into two categories like DOTA 2 does with it's unreliable and reliable gold system.
For instance if you kill a boss and obtain lets say 10k souls from them, and 3k from "trash" and you die, you only need to go pick up that 3k. That 10k would be soulbound to you. But if you buy something the reliable gold/souls gets used up first.
Icefrog created it, it's an ingenious system that could work for Dark Souls, which pretty much eliminates any legitimate need for a manual save system.
Add that, a single warning shot for NPC's to make an accidental hit less game ruining, then my main gripes about dark souls is gone.
You can't really ruin a game in DaS, since no NPC is essential. You might get the bad feels and lose some items, but you can always complete the game.