Hi,
NFC tag element is to be released this week if no last minute issue is popping up. We are finalizing the server upgrade as we speak. You will then have access to the NFC tag element and we will provide a project example for you to rapidly understand how it can be used.
I am not clear why you would need I²C element specifically, as the idea of using elements and Rapid IoT Studio is to 'hide' this complexity for users so they do not have to take care of managing I2C bus.
For example if you open the Weather Station demo project and check the Temperature/Humidity characteristics:
you will note that the temperature sensor has a preset I2C address corresponding to the hardware wiring inside the kit as on following screenshot:


This means that Rapid IoT studio is acutally managing and generating the code for you so that you do not have to bother about managing the I²C bus messages.
If you check the characteristics of the trigger connecting the sensor to the BLE characteristics you will see it is a read operation:


What this connectors does is to trigger an I²C read of the sensor, extract the humidity information from the full I²C message and post it to the corresponding BLE characteristics.
Regarding MCU Xpresso code for the NTAG element, we will open a dedicated thread and prepare a stand alone project example. By then I encourage you to check the code example here:
https://community.nxp.com/thread/485465
I²C function is being used in there and this example is coded fully in MCUXpresso