I don't think they will do an Edge +. Mainly because they made the Edge a 5.5 screen already and then they will be releasing the Note 6 later which will cover their 5.7 screen.
So why would the s7 edge sell much better? It's only .2 inches smaller (screen size), although it's much more ergonomic and comfortable to hold. It looks like Samsung is trying to cover their bases in the 5 to 6 inch range - S7 at the low end, s7 edge in the middle, and note in the 5.7 or 5.8 inch range.