I'm late at the party. I agree with the position of @fiatjaf, @ hodlbod, @semisol, @Cameri🐦🔥 and many others: no new kind for kind-1 edits.
However I like the patch idea, for small edits/addendum. It could be implemented as a simple kind-1 reply with a special tag. This way it would be always visible in the same thread; clients can choose to use it to overwrite the parent and let the user inspecting the history. In this case they should also manage (merge?) replies and reactions.
But to make it usable on every client the patch format should be really simple and understandable in plain text, something like like a quote (>) paradigm. This would also permit to use the edit manually on clients that formerly doesn't support it.
Examples of edit and append:
~the bat is on the table
the cat is on the table
+PS: the original source is xxxxx