They just need a beefier handheld with a HDMI port on the back to plug into your TV. That's all Nintendo has to do. Maybe a small port on the front for a controller jack or two. Or have a wireless controller.
Make a modular system that plays a clearly second tier in graphics level of games on par with handhelds that you can buy a couple of peripherals (or none, just an HDMI cable) and you can play it as if it was on your TV. The touch controls can go away, or you can leave the bottom screen stuff... on the bottom screen of the "controller." Add in a Nintendo style Console Caddy stand for when it is being used as a console, and have the HDMI port override the top screen and a wireless/wired override for the touch screen features/controls when plugged in/connected. Voila. You now no longer have to have two different devices, Nintendo doesn't have to support two clearly different demographics individually, and finally people can play pokemon without having to use emulation software or a handheld to do it.
Too bad I don't think Nintendo thinks that way. The NX might incorporate some of that, but I doubt they are going to make it that easy. I fully expect lots of stupid gimmicky shit, which Nintendo has been known for.