@Stark If it did, then #Lemmy would be the only project in the #Fediverse whose posts #Mastodon rejects or truncates if they go over an instance's character limit.

Longer posts are known to get through from all other known projects, so I wouldn't worry about that.

And #Discourse won't federate entire threads with all posts into the Fediverse, nor will you be able to participate in a thread on Discourse from Mastodon. It'll only announce new threads, i.e. what you'll get is the thread title with a link to the thread. If you want to join the discussion, you'll have to visit the forum itself.