Bungie really likes using threes whenever possible, so adding three new elements, for a total of six elements, is unlikely. They may do something like that in the next Destiny (if there does come to be one) but they would be more likely to go for nine elements at that point, or three groups of three as they would look at it. Still, all speculation is just that, until proven otherwise. Would be nice if they covered more in their weekly updates that what they do, I would like a teaser here or there to add some spice.