Well, if they improve radiant A.I. even more. Which I'm sure they have. I would much prefer option 2. Can you imagine? You're in a cave fighting some bandits then you get a message: "With this person's death a thread in the prophecy is severed. Revert to a previous save or continue in the doomed world you've created" (paraphrased) because Mr. Important to a quest line went and got himself killed by wolves while talking a stroll.
So, mortal to the player, immortal to everyone else.
Never had that problem in FONV. (The whole NPC dropping dead somewhere randomly)
And besides they kept only one character unkillable because you literally can't get to them just yet.
Then you could kill them
Just as long as the devs are clever about placement it should be fine.
I want my command humanoid spell to help non directly kill someone important.
I support killing anyone by everyone.