to cycle through the elements is one idea of interest, yeh... My own idea was to split Blue Mage DPS into various styles. like instant damage versus DoTs, and also if Blue Mage could specialize into a certain element, to make DPS styles like to split Blue Mage into options like various -mancers, in this case being Aqua-, Cryo-, Levin-, Pyro-, Terra-, and Ventus-; as well as if Blue Mages could specialize into the "no-aspect" or physical damage spells.
Blue Mage has the potential to achieve real in-class diversity, if Squeenix would just allow the dev team to do it...