Here's an interesting benefit this has over inline markup languages: it's natively compatible with text-based CRDTs. Normally, collaborative rich text editing is a strictly harder problem than plain text editing [0]. This is because there is extra structure (e.g., if someone puts a beginning "*" bold in the middle of a sentence, and that sentence is deleted by someone else, then you might end up with an unterminated bold sequence).

But if you swap out inline syntax for per-line syntax, then it seems like plain text CRDT should be enough for collaborative Aftertext editing. Pretty cool

[0] https://www.inkandswitch.com/peritext/