A few Off the Bat Thoughts about the Mechanics
Tags
I can totally see nsfw.nude work, but do you think tagging will be done much further? It's relatively much work to tag a thing well, maybe some sort of cross-posting is more rewarding to the user. Essentially it might be the same thing, but the act of sharing to another tilde feels more rewarding than adding yet another tag.
Hierarchies in Tags and Tildes
Yes! I love hierarchies for how they scale.
Do you think the one-dimensional nature of such a "taxonomy" will get problematic, or is it merely a corner case? I might have "food > recipes" and "food > restaurants" or I might have "recipes > food" and "recipes > chemistry". Again I feel like cross-posting is essential to solve this duplication issue. Maybe this as another chance to improve on reddit: if cross-posts just reference a single post there would be just one big discussion.
Cfabbro is part of the team? "We were actually considering allowing multiple ways to access the same groups. E.g. ~literature and ~lit going to the same top level group" sounds good.
Comments
I think "most votes" has a strong bias towards early comments. Ideally you'd give a new comment the reason of doubt, and make it more visible until a good rating about is has been established. For this you'd have to track up-votes per "seen".
Sadly it's really hard to track these implicit down-votes ("read but not up-voted") and generally it obfuscates how the site works. I still think it's worth thinking about, especially if you might derive trust/reputation from the up-votes at some point.
Otherwise commenting on rising stories is the an easy way to farm karma (I tried it on HN to see how the down-vote mechanism works, which is unlocked at 200 karma). Here I also agree with you, that this process should not be 100% automatic.
Group-specific trust
If tildes are nested, will reputation (eventually) be inherited up the hierarchy?
Filter-Bubble (found your opinion in some discussion about it):
I agree again, good communities are bubbles. I think the "no-downvotes" will help a bit so controversial stuff can rise.
Links
I also like your decision to not allow text on links. I really like how HN moderators improve link-titles sometimes to get rid of clickbait or inaccuracies.
I will give some UX feedback later, when I got used to tildes a bit.
HN mods can be overzealous though - I once posted a motorsport article, changing the title to make it intelligible to non-motorsport fans. It got quite a bit of attention but the mods later changed the title - even though my title was not clickbait in the slightest - to one which was basically meaningless unless you happened to be an F1 fan.
Yes, that's the main drawback of hierarchies: deciding where to place a new group, deciding on which group to post a message when the hierarchies is very developed into specific groups and your message contains a few different aspects (and deciding what to do when the subject unavoidably drifts from the original subject, but that problem is less pregnant on Reddit-like sites than on Usenet because uses have changed in between, shifting from one community posting on every group depending on the theme of their post, into more independent and split communities who tolerate more off-topic posts and comments in their own group).
Crossposting is very useful to solve this kind of decision problem, but on Usenet it was often frown upon. At least it was frown upon when no fu2 to a single group was set, if I remember correctly. Also sometimes a real crosspost is better (one single shared post/thread), sometimes a multipost is better (the original post content is the same in each selected group, but the threads then evolve in complete separation) because it avoids "culture shock" between several communities.
I wonder if there will be something like Usenet fu2 ("follow-up to") as well (if it makes any sense here?).
The decision problem (at creation time and at posting time) is less of a problem if there is a dictatorship model for group creations, and a pro-active moderation for posting (capable of orienting misguided posters to the right place).
Cross-posting was used by some troll groups as an attack vector.
I don't think this would work against Tildes.
http://faqs.cs.uu.nl/na-dir/net-abuse-faq/troll-faq.html
I think that a technical measure to mitigate this kind of abuse was to allow only something like a max of 3 newsgroups for crosspost without fu2, and 8 with a fu2 (IIRC). As any technical measure, of course it could not eradicate this kind of trolling completely, it just forbid the most abusive ones. Not sure if it was a Usenet-wide rule or just on my hierarchy.
the "culture shock" problem is very real indeed. Though I only have anecdotal evidence, twitter is a good example. A retweet leaves the realms of the intended audience and gets totally misinterpreted¹.
¹ e.g. this one. https://www.nytimes.com/2015/02/15/magazine/how-one-stupid-tweet-ruined-justine-saccos-life.html (I think it's even ironic and therefore against racism)