I'm currently looking into possible solutions for wall switches with high WAF;)
According to my wife, I'm already quite close, so I want to share my current project status with you and thank all contributors to MySensors.
My wall switch is mechanically based on http://haus-bus.de The multi push button switches integrate nicely with the Busch Jäger Reflex SI switches, I already have at home.
I created my own electronics based on the nRF52832 module from Ebyte.
Besides the Ebyte module, I only have inductors for DCDC mode, a CR2032 battery and the switches on the PCB. The switch cover is semi transparent, so LEDs might be added to give some visual feedback.
With the CR2032 battery the PCB is quite shallow, so I was able to extend an extisting conventional wall switch by using a double frame.
My measurements show a sleep current of 12 uA, so the battery should be good for about one year. However the nRF52832 should be capable of much less sleep, so I still need to work on that issue.
If anybody is interested in some more details, I'm happy to share the information.