The complexity line is that you are going to run out of RAM. ESP8266 and RT5350/ MT7620 /AR9331 are complementary to each other, not substitutes. I would never put an AR9331 inside LED light bulb, but I would put a ESP8266 in one. I would never attach a Zwave controller to a ESP8266 and try to manage a Zwave network, but an AR9331 has no problem doing that.
The complexity line is that you are going to run out of RAM. ESP8266 and RT5350/ MT7620 /AR9331 are complementary to each other, not substitutes. I would never put an AR9331 inside LED light bulb, but I would put a ESP8266 in one. I would never attach a Zwave controller to a ESP8266 and try to manage a Zwave network, but an AR9331 has no problem doing that.