I've just recently discovered the esp8266 and the world of IoT. I have an Arduino based project involving a couple of ACS712 current sensors and various other sensors.
While I realise I could move everything on to the esp8266, I'd rather add wifi capability to my current Arduino project in the first instance and also the ADC on the esp8266 looks a bit more complex.
To communicate using soft serial between the Arduino is flashing the original firmware the only option combined with the appropriate level shifters of course.
Regards,
David