From what I’ve seen, the main difficulty with Sonoff is that we’ll need to get the Pi to connect to the WiFi network the Sonoff device creates during its pairing process. Doing this is incompatible with all the other pairing processes that would normally take place at this time (e.g. the philips hue and tp-link adapters both expect to be talking to their devices over internet).
I think the most likely approach for now is to create a utility which pairs the gateway with the sonoff independently so it doesn’t mess with other devices.