Alright so based on your linked info it would seem they are developing a console and a new handheld. We may not know about the handheld immediately, but they may be announced at the same time because 3ds has been out long enough as well. Plus they upgrade handhelds all the time and there is little risk in showing off a newer handheld.
I think they are going the tegra route. I'm not sure, but how related are the gpu's for Geforce and Tegra(Maxwell /Pascal? OR how flexible is the Tegra line? Maybe Nvidia is designing a custom superpowered home console Tegra chip for the NX. I have an ouya, that was tegra, but that was like 3 generations of Tegra ago, and not custom. Nintendo chips generally are always special custom versions. I would imagine Nintendo might still pair it with an extra cpu even if it does have an SOC tegra. Maybe still another IBM PPC or an extra ARM.
Also, note Nintendo buys in bulk, is a new customer, and has excellent credit. This might give Nintendo some low prices on Nvidia's best tech.