I think it would be great if you could design a small esp8266-based switch module, possibly versions with dimmer as well, that can be installed in existing in-wall switches for EU/US standards. This way you can keep the existing light switch for manual control but add the possibility to remotely control the light switch via WiFi.
Similar modules are available today for z-wave and other wireless standards, this is an example of such a product:
This would be great! I would probably place one behind every light switch in my home. Unfortunately the sonoff touch doesn't look good in some rooms...