I think the 'progression of sin' makes sense.

if we limit it to just wrath, what are your thoughts on how we differentiate the characters?  I suppose rather than the elemental differences being tied to the sins, they would be tied to the individual Rias themselves?  The Rias themselves would have a wide array of differences with respect to the powers they impart on their hosts.  If we go with that, would we want to theme the Rias in a certain way as an added layer in addition to them being fueled by wrath?