I don't think anyone is looking forward to an iphone 7s lineup. Iterative designs are not going to sell. The newly designed iPhone 8 on the other hand from rumours will move like greased lightning.
The S variant needs to be the rumour that doesn't happen imo. Having three designs is just not a good choice, sure less retooling but people won't do 4 years of this old design and the new one is cutting edge. All apple buyers can afford the same device if apple only put all its eggs in the new basket. Splitting it up again is only going to add to the production costs of the new design. I hope I'm wrong.