for me, 4, 6, 8.
4. If you can distinguish sort of the things, it is spoiler. In Witcher, I was surprised Ciri's fate is determined by my very subtle, little actions. and those were undistinguishable. I really enjoyed it.
6. same as 4. It's spoiler, and break immersion.
8. I want to roleplay as I am, not as a character determined by some programming codes or numbers. when I chose threatening dialogue, then NPC should react naturally whether my threaten was successful or not according to intention of writer, not react awkwardly like desperately try to say that 'your threaten skill is low so I react like this!!'
I mean, if my threat failed cause my skill was low, It break immersion immediately. because the situation is not accepted naturally. instead, some thought occur like 'damn, I should have invested in Threat.' this is called immersion breaking. at least for me.
Now I sense some old rpg fans think like "What!? How is this immersion breaking!?".. many RPG were developed for intention for mimicking P&P RPG. but I think It's outdated design. of course some limitation based on stat could be good for gameplay wise. for example opening door by strength, or fixing the gadget by your engineering skill or etc.. but in dialogue, and social wise, It also could be immersion breaking feature.
If I should persuade some NPC for story progress, It should be designed naturally. the situation that I can persuade a person immediately because my character has high social skill is very unnatural. you should persuade the NPC through *YOUR* own wit, or real toil. not just by character's stats. and Witcher 3 accomplished it very well. for example If you want to know where the Dijkstra's treasure is, *YOU* should act really carefully. there are not options immediate passing skills like persuading. If you did something dumb just one, then you couldn't find the treasure forever. It's really on pins and needles experience. by the way, instead, if you could persuade him to tell where the Dijkstra's treasure is by simply choosing [Persuade him (Speech 50)], would have it been fun? Absolutely not.
To conclude, in dialogue, It shouldn't be limited by skills especially social skills (threaten, persuading, speech, seduction, whatnot). I think some technical skills like engineering or hacking is okay though.