this is their handheld replacement despite their insistence it is not. i don't see this getting traction with the old wii audience but nintendo's core portable and home console audience that bought 3DSs and wiiUs will likely buy.
i'm going to say ~50 million.
1 device means removing redundancy on those that traditionally buy both devices.
handhelds are dying so the portable would have been down 10-20% regardless.