The null consumer filters match any events, so they effectively ignore the
consumer QoS requirements.  For applications that only have disjunctions it
could be more efficient to perform all the filtering on the supplier side, i.e.
exploit the information about the supplier publications to build the exact set
of consumers interested in a particular event type/source pair.
This will require a consumer filtering strategy that correctly implements the
can_match() method, but whose filter() method is trivial.