I read somewhere that BSD was hurt by the confusing Unix lincensing status at the time Linux was growing in popularity.
Good point! I was thinking more like spec authors should add a compatibility layer on top of ActivityPub (which I don't know much either) where clients can subscribe with different synchronization styles, something abstract like mastodon-like with N characters max-length, or lemmy-like, or diaspora-like, or pixelfed-like... This way lemmy developers can decide what makes sense to expose in each sync mode or even stay hidden for some types of social networks...
The idea is being efficient with memory and network resources and don't sync anything not required. I think it would be a little bit like your latter proposal but more over-engineered :D
Uff fetching comments without any context doesn't seem that useful to me. It would be great if Lemmy only delivers the top-level post with a link to the full thread if it detects the client is a Mastodon instance.