Is ESP32 (including SDK) stable for making commercial products?

I'm not sure that just saying that because Espressif has shipped 100 Million ESP32 chips is the best answer to the question of whether it is stable enough for implementation in a product. I will say that my company is using it, but the newness of the chip has definitely added some hurdles. However, I do believe it is stable enough for use in products. I'm not sure if you were using the Arduino libraries or the IDF, but my experience with the IDF has been pretty good.

The ESP-IDF v3 (which is currently in pre-release) appears to have added substantial stability as well as opening up new features such as Light Sleep. I would recommend implementing Over The Air updates if you plan on using wifi, just in case though. That way you can update your customers' firmware if you end up finding any bugs later.

Something else to consider is the amount of documentation on the chip and the idf that you'll need. Both are pretty well documented, but I've ocassionaly found myself wishing there were more examples or guides for some function sets. The documentation is definitely improving though, so as time goes on this will get better. Espressif is extremely active on the ESP-IDF GitHub.

Also, the chip has had a couple of silicon revisions, so that may be something you want to look into as well to see if anything revised will hinder you in one version of the chip vs. another.

You can check a lot of this out for yourself in the ESP32 Docs: https://esp-idf.readthedocs.io/en/latest/index.html and ESP-IDF GitHub: https://github.com/espressif/esp-idf

Side-Note: I don't agree that this should be posted in arduino.stackexchange.com at all... Why would the fact that the ESP32 has Arduino wrapper libraries make this specific question only relevant to the Arduino Stackexchange?