To be fair, Nvidia is the only company around offering off the shelf SoC solutions suitable for a handheld, so it shouldn't be all that surprising that they'd be in the running. The only reason people (including myself) have been discounting them is their poor record when it comes to their relationships with console makers.
A few things to note if it is Tegra:
- The only Tegra products which support Vulkan are the K1 and X1. Either would have to be clocked down compared to their current use cases (tablets, some actively cooled), but would still be significantly higher in performance than I would have estimated from an NX handheld. There's also the possibility that Nvidia would want to use the NX handheld as a showcase for its upcoming Pascal-based "Parker" chip.
- Releasing an AMD-powered home console and a Nvidia-powered handheld would be odd, but stranger things have happened. I would wonder why, if Nvidia was so interested in doing a deal, they wouldn't have used Nvidia chips for both, but perhaps it's just a case of AMD offering better bang for the buck on a console chip and Nvidia on a handheld chip.