Sergey Kiselev designed this I2S Audio pHAT:
This is a Raspberry Pi Zero pHAT form-factor I2S audio interface board based on a Cirrus Logic (Wolfson) WM8731 audio codec. It provides line input, line output, headphones output, and includes an on-board microphone.
An update from the USB DAC + Headphone Amp project by Yin Zhong (summivox):
Months into the project and I was still amazed at the lack of availability of a class of ASICs: USB-I2S bridges. Well I just lied — if you are fine with USB 1.1 and USB Audio Class (UAC) 1.0, which severely limits your (bit depth × resolution × channel count)
So I kept looking for ASICs, and I found one that is close enough: XMOS XHRA-2HPA. It even comes with a reference design that does exactly what I want!
summivox has shared the board on OSH Park: