... They inexplicably (i mean literally, why the hell would they do this!) churned out the D5 with rubbish low ISO dynamic range.
I suspect the target audience doesn't really give a stuff about the extra DR

- it isn't as though it really is rubbish as you say

it just isn't as good as the D810. Sports and journalists need better DR at high-ish ISO's and this is where the D5 excels. Horses for courses. If you want the best high iso performance get the D5, if you want the best DR get the D810, if you want the currently best allrounder then it's a toss up between the D810 and the D750.
Surely they won't continue this approach for future D750 / D810 iterations? Bearing in mind that both those cameras were lauded for many things - but with dynamic range at low ISO being chief amongst those.
They won't for sure with the D810 successor, this is the high MP, high DR (read that as studio/landscape if you want) camera where ultimate IQ is the objective. If, and it is probably a big IF too, they decide to make a "true D700 replacement", i.e. a D5 in a D8xx sized body, then yes, they will use the D5 sensor.
The confusion for many (well for me anyway) lies in Nikon's roadmap. They need to clarify their plans re the FX range, having a high MP body with the best possible IQ is essential, as is having the top line sports/journo blitzkrieg machine. It's the other bodies that need consideration, do they have a D5 in a D8xx body? if so do they still produce the equivalent to the current D750/D610 (but only one ...)? I think they need to. They will almost certainly produce another Df too (hopefully with something like the current 24MP sensor and still NO VIDEO

). There is also some talk of producing a 5DX ... confusion reigns.