Although it should not be too difficult to make the MQTT Gateway with WiFi work on hardware and software level it is a bad idea on system level:
WiFi and MySensensor NRF24L01+ use the same 2.4 GHz band and with the antennas close a transmit from one will block the other and vice-versa.
Hmm dont really remember, but I think this was the solution
ntruchsess created this issue in knolleary/pubsubclient
PubSubClient.h:72: error: section attribute not allowed for ‘<anonymous>’