@eerke - Yep. I’m looking at a MCU that has ANT+. WiFi, BTLE, Zigbee all on the board. I’m thinking small box which you connect to USB for power.
Your Sonoff devices use the ESP8266 so yes, this is the sort of device (as well as the Shelly) I have in my house.
Now…if someone could hack a Withings temperature sensor and have that aimed at you while you workout and broadcast body temperature as ANT+ ! 