WPUNIGUIDE says that they must have an article but that directly conflicts with WPN so I ignore that part of the recommended guidelines  I understand your reservations about not having a hardandfast rule but there arent hardandfast rules governing the other sections of articles and things seem to work ok  If there really are enough interesting alumni that the list grows too long then just split it out into a separate article  And we can all object if someone adds one or more alumni that are clearly minor figures that shouldnt even be mentioned in an encyclopedia article