Mr. Maurizio Messa, you've touch very important problem. I have the same interest to use I2S' Audio Codecs, because USB audio cards is not convenient choice. USB jack only one and it should be reserved, for example: usb-disks, service modes (firmware update), etc. And most of high-level applications need sound to be more interactive. It's one reason to use micro-computers same as Omegas and Linux-based OS that has many trivial drivers to use. I want write my high-level user-space application with DB, Network, IoT, Audio, etc. as Windows Win32 and I have no need understanding of kernel-mode and other low-level infrastructure. I can use for it STM32 Cortex's MCU's but it's need many trivial issues that has been made in Linux.
I think The Onion Team should make new Audio Shield with audio driver because it's regularly application demand.