I think you could just upload the N3WiFi firmware to it, and it should work.
By the way, you could make it super, duper small if you chose to get the MCU in a WLCSP (Wafer Level Chip Scale) package. That's a chip form factor that basically does away with the plastic around the die (the actual silicon wafer) and just puts a thin layer of plastic on top and some solder balls on the bottom. I think that MCU in the N3WiFi is like a 1/4" square in the WLCSP.
Could be pretty cool. And _very_ small.