When you think about it, the core of the original Famicom is a pretty compact PCB. Take away the RF/Power board, disconnect the controllers and you have a base for a portable system. Right angle the connector, add DC power supply circuitry, an LCD module and then design a case around it with a controller PCB.
It's still too big for a portable I think. The normal NOAC portables are a lot more portable and are already great, who cares if they have a few certain incompatibilities.
I'm planning to make one soon. I have all the parts here waiting. Not a fan of NOAC clones and I've been wanting to build my own portable for a while.
The hard part will be the housing design, I hope to made it fairly compact. Shouldn't be too hard to get it around the size of a Game Gear or Nomad.
I'm glad someone is willing to Ben Heck the Famicom. You could put a 72-pin connector in their instead for a NES, it just requires some rewiring. The Famicom system board is not that much longer than the larger Famicom carts or the NES carts, so if you have the cartridge flush and parallel with the board, it should not look too enormous.
It's definitely not too big, here's the PCB without the RF/power board. My hands aren't huge :)
(http://s1.postimg.org/fzvxonyi3/IMG_20150830_103030795.jpg) (http://postimg.org/image/fzvxonyi3/)
I wanted to make one, but what stopped me was the display. I ordered one small from china with composite input but although my Wii displayed fine on it, it wasn't working with famicom. I'm not an expert on displays, so I only guess the problem was resolution.
So if anyone knows about cheap small 5V powered display please let me know.
You have to find one of these portable dvd players. Every now and then some of them with broken hinges or lasers show up on auction sites.
I bought this thing, though cheaper:
www.ebay.com/itm/3-5-LCD-Car-DVD-CCTV-Reverse-Rear-View-Camera-Monitor-/370867579478?hash=item56596e2a56
No good for famicom...