Doesn't affect (1) at all. As Sam mentioned, this is formalizing the de facto structure that's been in place a long time, so that announcement doesn't come with any changes to how HN works.

(2) Absolutely. Users can vouch for anything that's dead, including [flagged] and [dupe]. I see the notational confusion there; will ask Sam to update the post.

(3) Probably, but I'm not sure I agree with the line you're drawing from vouching to banning. Today's release massively lowers the cost an account of being banned. Instead of having your comments always stay [dead], they're now up for review by your fellow HNers; the community can decide what's good and bad. I'm not sure 'banned' is even the right word for it now— 'under moderation' would be closer.

The reason I say 'probably' above and not simply 'yes' is that there are a ton of issues to consider about it.