You don't need type-C for running an external DAC/amp. Most smartphones support USB-OTG over micro-B and many DAC units use generic audio drivers.
Of course you'd still need two ports if you wanted to charge at the same time.
It would probably be more interesting to see smartphones that could use the headphone output as a digital signal, like a coaxial output. We want the 3.5mm output anyway, so why not just let it dump a digital signal to an external amp?
Most people probably wouldn't really care for this, and the ones who do probably have portable media players already, so I would prefer to keep the headphone jack. The reality is, though, that USB-C appears to be the future.