Iwata: Our next system will “absorb the Wii U architecture adequately”

[Soundwave]

My guesses ... at least two (maybe more) hardware variants that are both reasonably cheap and use fairly powerful, yet cost efficient mobile (smartphone) components. Nintendo will be able to get a very good deal on these chips especially if they are reused for both machines (buying in bulk):

Nintendo Mini-Gaming Tablet (Fall 2015 Release):

$199.99 launch price
Quad-Core ARM CPU
Dual Core PowerVR G6430 (clocked at 500 MHz/core)
2GB RAM (1GB for OS)
Approx. 200+ GFLOP system performance
5.7 inch 1280x720 multitouch single screen w/stylus support
Can run downgraded (540p) versions of Wii U titles and upgraded, reworked (HD) versions of 3DS software
Easy to port iOS/Android apps
Mario Kart 8, DKC: TF, Monster Hunter 4G HD, Luigi's Mansion 2 HD, etc. available on day 1.

Nintendo Micro-Console (late summer 2016):

$169.99 w/a Wiimote like controller.
Quad-Core ARM CPU (same as tablet only higher clocked)
Quad-Core PowerVR G6430 (full clocked at 650 MHz)
Approx 650 GFLOP system performance
4GB RAM (1GB reserved for OS)
Can run most games at 1080p (some may have to settle for 720p)
Summer 2016 release.
Same games as Nintendo tablet, unified accounts.
About the size of a deck of cards, no disc drive.

So the console is actually the cheaper version of the two, even if it has a better chip, chipset costs aren't that big of a deal (no LCD screen/battery costs allows it to be sold for cheaper).

Plus only $169.99 to get into this Nintendo ecosystem is not a bad price point at all. Keep things cheap.