Not yet, unfortunately. Mostly due to protocol limitations—we use AT (https://atproto.com) for federation.

can tangled support a forum-styled or subreddit-like thread discussion interface, on a per-repo basis so that "anyone could start a subreddit" via creating a discussion-only repo?

Wondering if something like this could be implemented on tangled with public-inbox:

https://public-inbox.org/README.html

> public-inbox implements the sharing of an email inbox via git to complement or replace traditional mailing lists. Readers may read via NNTP, IMAP, POP3, Atom feeds or HTML archives.

> public-inbox stores mail in git repositories as documented in https://public-inbox.org/public-inbox-v2-format.txt and https://public-inbox.org/public-inbox-v1-format.txt

> By storing (and optionally) exposing an inbox via git, it is fast and efficient to host and mirror public-inboxes.

We’ve considered this a lot. Our issues implementation is threaded—perhaps more Stack Overflow-like. We’re thinking of renaming it to Discussions, and having the actual issue tracker be collaborators-only.