Stereo I2S To USB Audio
I have searched for a way to convert an I2S stream to USB audio ...is it possible?


I think you are thoroughly confused at the difference between a control channel/device driver, a data format and an interface. 

USB Audio as a spec does NOT specify the data format. It is a USB based control system for Audio output and input. See the USB Audio 3.0 spec here, and read Audio30.pdf within the zip file. 

This will explain that USB Audio can 'control' endpoints that consume either analog or digital data.

Read further into Frmts30.pdf and you'll find that you could transport PCM (I2S uses PCM audio format) over the data channel and consume/convert in an endpoint of your design ….all controlled by USB Audio.

I2S is the interface definition for clocking PCM data from one chip to another. NXP have not maintained a spec in many years, but many others keep updating it, this definition from Cypress does a good job. 

So there is NO conversion for I2S to USB Audio since I2S is a data format and USB Audio is a control system. 
You could extract the PCM audio data from an I2S stream (but there are chips for that), and I'd bet you already have the data stream in a PCM format somewhere in your system.