Thanks.

1. Is it possible to put this under ignore (or mute)?

Ignoring hides a user's posts. Muting them prevents them from commenting on yours. Currently, both do drop the user's comments to the bottom, like hush. If we implement Hush, we will actually be separating the functionality. The reason being, that each function serves a purpose, and the purposes often don't overlap. I would hush users that I would not want to ignore. I do ignore users I do not want to mute. Automating is very difficult, because you will always create an artificial bias based on your assumptions and limited knowledge.

2. It needs to be easy to un-hush someone.

I'd like to start with it being the same as ignore/mute. Highlighting their status might work against the functionality. It's fairly quick to toggle, just click on their name, and then click the toggle button.

3. With three ways to negatively impact a user's visibility, I think it would be nice to have positive impacts. I was thinking about a 'relation number', a factor to indicate how much you vote on someone.

I'd argue that most of the site does just that. You follow people, share their posts, vote them up, and badge them. There is currently a setting called 'share-counts'. If you toggle it on, you can see how many times you have shared a user's posts by hovering over their name. (BTW I recently added a link with explanations for the settings) But even there, I think we would be assuming too much if we used this as a signal to sort comments. A very good new commenter would be biased to sort beneath an average one that you had shared some posts of. IMO the need for the bias to degrade indicates that it has fundamental issues that need to be mitigated.

4. What is the main goal of the improved comment sorting?

I see two primary goals: 1) to add a user-specific customization to comments that is similar to those applied to the feed that results in a better experience for that user, 2) to enable an individual moderation effect that leads to a higher quality site overall.

do you want to simply nudge comments up or down a bit, or make comments rely heavily on the interaction between the user, or something in between?

Hush would only nudge down the ones that were selected as poor, and only for that user. Voting and discussion will remain the way to nudge up the good ones, and that will remain shared. As with the rest of the site, positive signals are public and generally have community effects, negative signals are private and generally have individualized effects.