I have probably spent a third of my life in studios, about half of that in all-digital environments and have never encountered I²S outside a development lab. Which, of course, makes it ideal for selling to audiophile suckers.I2S and AES are not very familiar as connection methods for consumer audio equipment, but they are standards that are often used in professional audio equipment such as stages and studios
AES (with external lock to a master clock source) is the de facto standard.