So, DHKs were introduced because players were camping towns/quest givers at the launch of the game in 2004 and preventing people from being able to progress. Blizzard needed a way to dissuade people engaging in this behaviour and the DHK system was what they came up with.
I agree that this system sucks and the fact that you can lose significant progress because someone accidentally pulled a civilian, or worse, decided to deliberately troll you by killing one, is terrible. However, I don’t think you can outright remove it without replacing it with something else. Otherwise we’ll just go right back to that same environment.
A common alternative solution I’ve seen is to just make those key NPCs not attackable, which absolutely does the trick, but I could also see it being a little immersion breaking. Can you think of any others?
I think this is a great idea.