Waking an ESP8266 from Light-Sleep using a signal from MQTT?
I was wondering if it would be possible to wake an ESP8266 from a request over MQTT while it is in Light-Sleep mode?


No. The ESP8266 has to be awake to communicate with the MQTT server.

The best you can hope for is a periodic wakeup to connect to the server and check for any new data.  But of course that relies on the data being set to QOS 2 so it keeps trying to be delivered until the ESP8266 is awake to receive it.