I do think that they will add that center glyph, and that it will be a "super" glyph. It just makes sense with the way that the glyph interface is designed and the fact that we have 5 more levels coming. I thought that back with the current glyph interface was introduced.
I am more interested in mastery/glyph combinations. What will the mastery talents be? Will they influence which glyphs we pick? We are actually planning on covering mastery a bit this week on episode 62.