Are you sure, it allows only to edit the last message, or is this only the implementation in popular clients? afaik it allows to edit any message that has a unique id.
@icedquinn This may change in the final version of the XEP. And in the meantime I saw clients with a retraction function (it's another XEP), which is also interesting.
On the other hand I noticed that people are surprised that you're able to read the original message. The edit function may be misleading when it comes to security.