Ignoring the idea that the NX detachable controllers could be something completely different from the dev-kits which I tried with the last two fan mock-ups here, I tried doing this.
Detachable controllers, on the top are the shoulder buttons in red. Black circles are the circle pads. The split D-pad is positioned just below the circle pad like how the A button was positioned below the D-pad of the Wiimote.
I went with making them symmetric so both circle pads are on top. Face buttons are below. The red face buttons are for the share and home buttons.
The black dots are for the speakers, this is probably important because I never saw anyone do this for the mock-ups. When in portable mode, the detachable controllers have speakers to provide sound. When docked, sound can just come from the TV so when you play in Wii Remote style you get sound effects from using items on the Wii Remote like swinging a sword.
The only question is whether the NX device itself would also have speakers if you just wanted to play touchscreen only games when taking the device without the detachable controllers with you.
Oh and the part on the right is showing the trigger button in green and the connector which I am trying to show is retractable so that it's not in the way for Wii Remote mode. As long as there is space inside the remote it can be done. No need for magnets.
Edit: I guess I forgot to draw buttons or something on the back to press to unlock the connector when detaching it.
Edit 2:
Now I just drew those detachable controllers and attached it to the NX. I also added speakers on the bottom of the device with regards to the things I mentioned. There are still speakers on the controllers but drawn like that of the Wii U Gamepad.
The NX has a very tiny bezel here assuming that this is what Nintendo has decided with the deal with Sharp for the Free Form Display assuming the deal hasn't been cancelled with Nintendo.