The ESP Easy firmware can be used as a generic Ser2Net gateway. This will bring serial communication to the wireless network. This will only work if the controller supports a lan connection where it will use 'telnet like' communication to the other end.
Domoticz has support for a few of those LAN gateways. The RFLink and Opentherm gateways are known to work with firmware R124 or higher.
WARNING: Applications that send large data packets like P1 smart meters do not work properly with the current firmware version. This may change in the future as it depends on Arduino ESP8266 core 2.4.0 development.
You have to connect the RX and TX pins of the ESP module to the target serial device.
Next use the device tab on the ESP Easy webinterface and create a new task by editing one of the available tasks. Select "Serial Server" from the dropdown box.
Enter the serial port settings that match with the target device and select the TCP port that the remote controller uses to connect to this serial server. That should be all.
You can test communication using the good old telnet tool, just connect to the ESP IP address and start typing. Characters should appear on the serial port. You can verify this using the Serial Monitor from Arduino IDE.
There's an option to connect a GPIO pin to the target device reset pin (must be active low). Once connected, the ESP will reset the target device during it's own boot stage.