There was a lot of chatter when the NX was first announced that the system might use ARM based chips, since there was a desire on Nintendo's end to be able to develop for their handheld and home console more concurrently. I remember thinking that if they were going to go that route, Nvidia could be a good choice, since they have GPU architectures that scale well from tablets all the way up to big desktop PC parts. ARM is supported in a lot of the 3rd party devs' middleware already, so the question would be more "is the ARM CPU fast enough?" rather than "can devs deal with a CPU that's not x86?"
Anyway, a little curveball in my thinking was that AMD has worked on X86 based tablet SOCs in the past, so it wouldn't be too crazy to think that they could produce a solution for a Nintendo handheld.... but, I thought something like an Nvidia ARM chip was a little more likely, if Nintendo really wanted to keep things easy with their internal development between a mobile and home device.
Who knows tho? I'm still skeptical about a Neo release this holiday season, since I thought we'd see 'Xbox One S' types of refreshes from MS and Sony this year, but not anything as substantial as what the Neo is rumored to be until another year out or more.