Is it possible? One connects to the CSI port and the other one to the GPIO ports and use the i2c interface to extract the data.
Only the official Raspberry Pi camera (or clones) can use the CSI port.
Do you have an I2C camera in mind? A camera connecting via SPI could be faster.
Why not connect a camera via USB? That's how a lot of webcams work.
The Pi's compute module with the I/O driver board is capable of driving two Pi camera modules and in the last few days the firmware has been enhanced to provide stereoscopic capabilities too. As that post makes clear though, this is for the compute module only, it'll never work on the Pi as only one CSI interface is exposed on the Pi.
It is possible to use the multi camera adapter for Raspberry Pi to use two cameras.