So one of the ideas, I've debated is a portable Wii. Stuff inside a wii-u controller case.
I've torn apart my old wii, because I needed to replaced the disc drive and it got me thinking, the console itself isn't that big without the disc drive. Wii's have been hacked to run games off USB drives and a viable project would be to condense most of the space. It'd be very plausible to take the hardware out of it, and adapt it to fit into a 3rd party Wii-U controller shell. Add a TFT screen (Hardware upscalers exist to bump it to HDMI). A wii controller could either be hardwired into the buttons of the Wii-U controller, even for virtual console games like the original mario.
I think the mix of modern generation/old generation could be a fun build.