Mastodon hashtags are not accounts and do not Announce every post and reply like Lemmy. If nobody follows you on external instances, your hashtagged toot will not leave your instance. On the other hand, if you mentioned a guppe group followed elsewhere, the group would boost you post to its followers.

Better (more Lemmy-like) discovery.

PieFed was able to subscribe to Guppe groups along with PieFed/Lemmy communities, Mbin magazines and PeerTube channels.

Threadiverse communities differ from following hashtags by having moderators who can remove posts or ban users. That provides extra value because that means people can’t post spam or off-topic things in them as long as the mods are doing their jobs. But if that isn’t possible, then why not just follow a hashtag and post to it?

Same feeling here.

I see good points in this comment, even if the analogy of their being like hashtags might be a little off.

gup.pe groups have a 1-word description. Most of them I've been unable to assign a topic to because I didn't know what the word means or it has ambiguous meanings. Most have no posts. So they land in the "unknown" topic.

I always wondered what I would do if someone started posting porn or hate to them. It would be a nightmare. I'd just have to block the group, I suppose.

Frankly, instead of someone creating a gup.pe-like group, I think they ought to create a community in PieFed, MBIN, or Lemmy. gup.pe was an early experiment when there wasn't a threadiverse.

I'm fine without gup.pe or gup.pe replacements.