ESP8266 - is it used in real industry?
The ESP8266 chip is relatively new to the market (circa 2014, I think). So it's short market availability has limited its adoption somewhat -- some early adopters have chosen it, but that's usually not a benefit to high volume, low cost designs. There are also many more well tested chips/modules that have better documentation and better support. TI, Silicon Labs, and Microchip all offer chips with similar features (each manufacturer even offers several different versions targeting specific design constraints).

One of the major selling features of the ESP8266 is its low cost (a huge benefit for the maker/hobbyist market). But when buying any of the other existing parts in large quantities (for mass production), the prices become pretty similar.

A quick search shows a few products that use the ESP8266 chip. There are likely many more products that use the ESP8266 as well, but their bill of materials is not publicly available. Here's two that came up immediately:

Sonoff Smart Switch, Ebay Light Controller

It's likely that the ESP8266 (and ESP32) will eventually be adopted by more and more designs, especially as the "Internet of Things" industry grows and engineers become more comfortable using them.