XEP-0091 is replaced by XEP-0203, so I added support for XEP-0203 (very trivial) without removing support for XEP-0091 for backward compatibility. See the attached patch.
I've noticed that in two places, the new element is added to the element, complementing the existing, older element. In pubsub/pep however, there are two places where the new element replaces the old element. Why was this done there?
The idea of the patch is that in future, XEP-0091 support will be dropped. Right now, it is only there for backward compatibility. Therefore, the new element complements the older one at any location where XEP-0091 was supported. However, at some locations none of the XEPs was supported, because a mixture of old style element names and new style date formats was used. In these cases, I decided not to start supporting XEP-0091, because supporting it does not give us backward compatibility.
I'm fine with that. I've applied the patch.