Coming from a SemiAccurate report, the NX is going to use NVIDIA’s TEGRA technology on the NX handheld. Reports also indicate that NVIDIA will take a loss on this deal likely so it will pay off on future NX devices (similar to the PS4k, New 3DS, etc)
On the other side, Emily Rogers released her own statement. She says the NX will not use x86 architecture and that the system will be (in terms of raw specs) between PS4 and XBox One, likely closer to XBox One. Though she notes that due to differences in architecture comparing pure specs doesn’t really mean much and performance could be higher though she doubts it.
UPDATE: Emily also vouches for NVIDIA on Nintendo’s future devices.