I think the biggest problem people (well, those who really care about the quality of the music) will identify will be that the audio DAC will go from being a (generally) distinct component of the phone to an integrated component of the USB-C driver. I believe this will likely lower the quality of the DAC (as the rest of the chip will be mostly, if not all digital components) and the overall music as a result.
IOW, you may still want to have a discrete DAC dongle for your USB-C phone.