First, would it be possible to add Quick Charge 4.0 capabilities to the charger? QC 4.0 will be compatible with USB-C PD so it is a superset of PD and will be included in next years Qualcomm Snapdragon 835 phones.
How big do you want it?
As small as possible
Do you want other ports to be able to charge other things with it? And if so, what kind of ports?
1 USB Type A at least
1 Quick Charge 4.0 capable USB-C port (See above)
Do you want data transfer through the charger?
Not necessarily but if it comes free I will take it.
Should it plug directly into the wall or should there be cable?
If the plugs are interchangeable to international standards (which I hope they are) then yes, otherwise no.
Should the wall plug be replaceable by the user?
Should it only include one localised wall plug, or should you get them all included?
Ideally the plugs are interchangeable
Should Eve put their logo on the charger?
Do not care
New Idea for an optional second charger:
Why dont you make a (second) charger work as a battery pack as well? Of course it will make it bigger but if it can store like lets say 20,000 mAh and charge both smartphone and USB-C devices with the proper amount of watts you not only have a USB-C PD charger, but also a USB-C battery pack, which are scarce still (I know of only one and that can only charge a 25 Watt MacBook afaik)