Another example of longer posts which are folded under a “read more” type link within the Fediverse itself can be seen in the Hometown fork of Mastodon (https://github.com/hometown-fork/hometown), which is running the hcommons.social platform. The admins have upped the character limit to 1000 instead of the usual 500. Ideally those reading in other parts of the network would see the beginning of a post and a “Read more” link to read the remainder of the piece.
I often post to my own WordPress website which has a plugin to make it appear as if it were ActivityPub compatible. If I follow it via a Hometown-based (Mastodon) server, like my hcommons.social account, I see all the full short notes/replies content which are usually 1000 characters or less. For posts over that limit, there’s a “Read More >” which opens up the entirety of the article within the hcommons.social interface where I can read it in its entirety. Naturally there’s a link to the original, so I can also go back to read that if I chose.
I’ve just gone over the 1000 character limit, so I’ll post this on my own site, syndicate a copy to my hcommons.social account, and with any luck it will serve as an example of how all this might work between WordPress, a forked version of Mastodon, and Mastodon itself, as well as for testing it for reading in other parts of the Fediverse if one wished.
Beyond this reading experience, one should also be aware of a separate user interface/interaction problem inherent in how Mastodon and potentially other parts of the Fediverse handle replies and who can see them. I’ll leave this link to explain that issue separately: https://fedi.simonwillison.net/@simon/109559268498004036. (Hopefully your instance will let you see a subsection of some of the replies to it…)
An additional benefit that one gets in bolting on ActivityPub the way it works for my WordPress site is that folks who subscribe to @email@example.com can see linked text natively from within Mastodon despite the fact that Mastodon doesn’t allow one to wrap text with URLs to link out.