Footage on twitter of Bairstow going through keeping drills. He may well do this every game but if he were to keep he cannot bat 3. Way too much pressure physically and mentally.
If Jennings doesn't play, it has to be Burns and Denley to open, Buttler at 3, then Root, Stokes, Bairstow (if keeping).
If Buttler is playing solely as a batsman, he has to bat three. Root won't and all others need to be able to focus on their bowling/keeping and maxjmising those skills. That means batting middle order.
All tbis assumes Foakes doesn't keep, which would be a shame