Hello! I'm currently designing a project based off of the Nintendo Switch and modern gaming tablets, It's called PiTab (Pie-Tab) and it uses the Raspberry Pi 3 Model B. It has two slots for controllers on the sides, and a screen in the middle. It also has a 3.5mm headphone jack, an HDMI out, and a rechargeable battery.
Why have a rechargeable battery? It's made to be taken with you on the go, not just at home! There's two ways to play; connect it to the dock, or play as a handheld.
You can also play with any bluetooth/USB gamepad supported by RetroPie.
I probably won't make the "PiCon" controllers on the sides of the console, as I'm not good at that kind of stuff...