I made a small project which is possible to connect up to 16 encoders on the i2c bus.
I used a small PIC microcontroller for doing the job.
With this board, you don't need to continuously polling the encoder, you just need to read the internal register for getting the actual counter value. There is also the possibility to add a PWM bi-color led.
Here you can find the main project description:I2C Encoder | Hackaday.io
I also posted all the documentation on GitHub:GitHub - Fattoresaimon/i2cencoder: Documentation, source code and examples about the I2C Encoder project
There is also a Arduino library and a couple of example
I made the project open-source and you can also modify the source code.