Surprised no one has mentioned Eguchi -- the guy who was the lead producer on WiiU hardware and oversaw EAD projects like Mario Galaxy and Mario 3D World. My impression is that he's pretty much in charge of the Tokyo office.
In any event, we pretty much expect some Japanese guy who's been with the company since the 80s.
I have little doubt that there are many potential applicants for the job.
Let's be honest, Iwata had some magnificent personal qualities HOWEVER did lack some finesse in actually running the business. I've loved Nintendo's independent direction, but I'm tired of the go-it-alone behavior.
I predict NX launches in 2017 - not 2016