With all this talk making it seem pretty much a fait-accomplis that McCullum will be no longer opening, I just don't see how he can fit into our middle order. Assuming Watling shifts to open you have Williamson 3, Taylor 4, Brownlie 5, Allrounder X 6, Ronchi 7 (unless you shift Brownlie to open as well, which would seem crazy to me). This gets even worse if Ryder is back, as suddenly you have Williamson, Taylor, Ryder, McCullum and Brownlie fighting for 3 middle order spots (or 4 if Ryder is used as our 4th seamer).
The only way I could see it getting easier would be if they make Watling open & keep...Then you have that extra spot at 7 for the All rounder, and then Williamson, McCullum, Taylor, Brownlie in places 3-6 (assuming Ryder doesn't return yet).
But it gets even worse if the reports of Peter Fulton as an opening option came about (dear God I hope not)
http://www.stuff.co.nz/sport/cricket/8178734/McCullum-no-lock-to-open-against-England