Is it possible to add an additional board on Arduino Web Editor (create.arduino.cc)? I'm using a board that can be programmed via Arduino IDE (a NodeMCU with ESP8266) and I've configured the Windows client successfully. I've added an additional board through "Preferences" menu by specifying its configuration url, following manufacturer's directions.

Now, I'm quite happy with the web editor, the one at create.arduino.cc, and I'd like to use it with this board too. Is there any way to configure additional boards?
No, there isn't.

The web editor is completely closed. It's a service run by Arduino, and as such it will only support Arduino's own boards. 

Two reasons:


Why should they spend the time, effort and money adding support for other people's products?
It adds value to their products to encourage you to use real Ardiuno hardware.


Business is business, after all.