Iwata said in his 2013 briefing that the next system after Wii U would absorb it's architecture, IMO this can only mean that NX will use AMD technology.
Eurogamer has been wrong about final Nintendo device hardware with the DS2, which they insisted was using an Nvidia GPU, but it ended up being nothing more than a placeholder for the 3DS's final processor.
The rumors about Nvidia don't make much sense, given that NVidia have outright stated that they are interested in the Self Drive and AI markets, but not the mobile gaming market outside of their GTX 1000 series GPU products being used in gaming laptops.
Nvidia hasn't said anything about making or stockpiling a bunch of Tegra X1 processors for some unreleased product or any other device, which would need chips in the millions for the release of a new device in 2017.
The rumors insist that Nintendo got some ridiculous at cost or loss making deal from NVidia, when companies want to make money, not make a loss on a product.
Nintendo would be the one in need here, not Nvidia, so it makes no sense for Nvidia to be begging for a foot in the door of dedicated gaming market.
NVidia has great relationships with 3rd party developers, they could just as easily release a successor to their last shield devices and get some exclusives for those devices to push them into the dedicated gaming space, but that hasn't happened, most likely they don't feel the market is worth it, given their own sales on tablets and other devices it makes little sense for them to really care about the market when they have bigger fish to fry, like expanding the gaming laptop market.
AMD have been a partner with Nintendo, providing them with their hardware for a number of console generations, it's been proven that IBM PowerPC CPU tech can be emulated on something as weak as an AMD Jaguar CPU and there would be basically no need for emulation of the Wii U GPU going to Polaris or some older GPU architecture from AMD.
14nm Finfet will be significantly more efficient than what was in the Wii U.
It's only Tegra X1 that's been rumored to be in these supposed NX Dev Kits, sure it's overclocked, but that doesn't rule out an AMD 14nm Arm processor being used in the final system.
AMD would likely be more cost competitive, they have more experience in the console gaming market, even Zen could be used in a console if NX has a more fixed home device, it could just be used on an MCM like Wii U's processor layout was.
AMD provides the technology for the competition, which developers appear to have been pretty happy with.
Overall there seems to be a lot pointing to AMD, sure Nvidia's tech is more powerful, efficient, but there's nothing official pointing to NVidia being interested or even having any actual ties to the dedicated gaming device market.
As far as I've seen there's no hint that any of the media have their own unique sources confirming Nvidia as the final SOC maker, they all seem to come from the same source.
AMD has confirmed they have a bunch of design wins for the semi-custom market, which basically confirms a dedicated gaming product or products that are yet to be announced are being developed by them.
NVidia would need to have confirmed any major business deals with such a company as Nintendo to their investors as this will effect their stock price, to not do so is holding back vital information that shareholders need to know and that isn't good business, NVidia doesn't like ticking off their shareholders.
Eurogamer, WSJ, etc are just posting rumors, they're not legit, they've certainly been wrong about this stuff and in order to buy their rumors you have to ignore Occam's Razor.
The simplest answer is the most likely, Iwata said the next Nintendo system would absorb Wii U architecture, Nintendo has a great relationship with AMD, they've used them for years, in multiple platforms and their modern tech also brings the necessary efficiency levels to put at least Wii U levels of performance into a handheld, if not more than that for a portable device.
Nintendo also doesn't bank on the most powerful tech per watt, even when their console requires low power.
Nintendo likes cheap technology.
Using Nvidia actually goes against all of this.
AMD makes a lot more sense for Nintendo.
