The current method is to set the 'requiredProperty' value in a SeasideFilteredModel to set the flags for the properties that a contact must have in order to be filtered into the model.  The cache has status flags knowing whether each contact has one-or-more email addresses, phone numbers, online accounts, and whether they have a global presence which is not offline/unknown (there is no way of requiring the 'online' status yet, but I plan to add it).