I see only one problem: who really need high end (open) headphones connected to smartphone? "Normal" person probably would like to have something cheaper, smaller (IEMs even) and probably closed to have on-the-go.
And if you are able to but high end headphones you probably already have some dac/amp.
It makes no sense whatsoever to use a flagship headphone with a smartphone. Flagships are made to be played out of high-end audio gear/amps...plus, you look really stupid wearing an oversized headphone out in the street...that's what IEMs were made for (as well as the Beyerdynamic DT1350s). The Ultrasone ed. 8 are small enough and can do the job, but even that is pushing the envelope!