I don't think he'll ever do it.
If Bmac wants to continue coaching (which to me is a big if) he will do so on the T20 circuit.
Look at Stephen Fleming - he should be the coach of NZ, but why would he give up his IPL commitments which pay him about NZD $1m for a few months work.
Gary Stead is paid about NZD $350,000 (easy to see why he has hung around) but typically being the head coach of NZ requires to be outside of the country nearly 200 - 250 days a year.
I just can't see Bmac coming out of a dual coaching role with Eng, earning mega bucks and taking up the NZ coaching role. Could be wrong but I suspect by then (if not already) he will be completely set for life and will go back to his first love of horses