I'm working on a thin implementation aiming at 1mm.  

A flex circuit with QFN devices should come in just under 1mm.

I've got a design and I'm waiting on the QFN MCU to assemble them.

In the mean time, I thought it might be nice to have smaller SAO version.  The NFC EEPROM and CH32V003 are available in SOIC-8 package that is easy to assemble by hand, and they both fit nicely inside the space of the NFC PCB antenna.  This will also make a convenient board for firmware development until the thin flex circuit version gets here.

8 pins on the MCU is plenty for an SAO.  2 pins for power, 2 for I2C, and 2 for the buzzer.  That leaves two for the RGB LED.  The serial controlled LEDs draw too much power to be useful with the NFC harvested energy, but you can drive 3 LEDs with two GPIO.  I used the same trick I used on my KUIIC board https://hackaday.io/project/183092/log/201387-full-color-dimmable-rgb-led-with-only-two-pwm-outputs 

This smaller version turned out great and the WCH chip can play a nice tune from the harvested power.  It also fits better in a pocket.  Design files are on github:  https://github.com/gsteiert/nfcwchsao