A device like this (with limited hardware buttons) would really benefit from in-line remote control support.
There are two control standards - one for iOS devices, and one for Android devices.
I've got some 3.5mm TRRS > MMCX cables, with Volume & Audio Controls, that have a mode switch, so they can work with either type of device. And, I have some VE Monk+ earbuds, that work to control Volume & Audio on my Android phone (Nexus 5). Neither cable will control the Volume on my Android Tablet (Nexus 7 (2013)).
People who have earphones from their iOS or Android device, will want the M0 to work with their cable.
I suspect that it's probably free
* to implement the Android standard, but I wonder whether Apple would require licensing to implement the iOS standard?
*When I say free, I mean that you don't have to pay licensing fees - but there is a cost to implement wired remote control, because an Analog-to-Digital Converter (or discrete voltage window comparators and DIO pins on the controller chip) would be required, to detect the different voltages that indicate the Play/Pause and Volume buttons have been pressed.
Another alternative is to use a quality Bluetooth Receiver, that has the controls on it, since it can send the control signals back to the DAP - and this would only require a firmware change.
I've got a couple of Bluetooth Receivers that can control all of my DAPs in this way - and the only DAP of mine that has Play/Pause (but not Volume) in-line control capability, is my Cayin N3 (Supports for CTIA standard).