I use MQTT with domoticz, Node Red, Alexa and sensors based on ESP8266 and RasPi. Most of the traffic is domoticz in/out, but I also have topics for Alexa and some of the custom sensors that are translated in node red to/from domoticz messages. Planning to add some MQTT for security (keypad, RFID) - with encrypted payloads! MQTT for SMS notifications is interesting, might look into that.