‘Pause and print in place’ type objects are fun.
Making custom NFC tags for a project, left a space inside the object, careful selection of Slic3r settings and pausing the printer just before the top layers to put an NFC sticker in place before letting it continue and seal it in. Whole object is just 2mm thick and 9 layers.
Need to do a filament change before the last two layers for better contrast, or upgrade my machine to dual filament. But it works well.
Awesome idea
Tried the same thing to create modern contact card - contact info written on bottom side, qr-code on top side, nfc inside.
The idea of these is people will get to make their own cards/designs if they want. And at the end they end up with a tag to let them sign onto the 3d printer system. 
Nice idea.