I think a full-fledged editing script would be most efficient (vs plain diffs). Could have operations like select, replace, copy, paste, movement, etc. Similar to vim commands maybe.
Need to be mindful of different scripts/langs. 1-2 bytes as marker in front of post could indicate the "dictionary" to use for compression. Could have several for each lang.
Would suggest allowing posts to me marked as "indelible" at creation to disable any future editing (in the event of a compromised key, etc.) via the suggested "edit" protocol.
Close. There needs to be an optional 'delay send' feature where it doesn't broadcast right away and you can edit/delete for 30-60 seconds before it broadcasts
Also! It would be a great chance to implement a queue of rejected transactions that hit the spam limit so they can auto rebroadcast after the next block!