I just realized that the default specifications for ActivityPub/ActivityStreams do not have a way to perform an update on an object's ID. (ie, moving it from example.com/1 -> example.com/2)
An Update activity does not allow ID updates because it would lose the reference to the original one. (It can be massaged by using an Origin property, but I don't like that).
Another option would be to use a Move activity (which is defined as moving objects between collections), where the Origin property is the object itself instead of a collection. (I like this behaviour better, as it requires less divergence from the spec)
