I'm firmly on team "dual USB port" for this problem. We do this on computers, which can then perfectly well charge and play audio at the same time. Why not phones? It seems like there's plenty of space for a second port.

the usb port is much more complicated than a 3.5mm port. It is more expensive, it takes more space. Do you add another real port or a built in hub? (they would go with the latter, probably)

The advantage is you have a backup port.