In short, I don’t think we’ll be offering card customisation from scratch any time soon. We’re still considering alternative options for card colour and design, it’s been discussed at length here
As far as possible we’d love to chop down the time it takes between ordering a card and receiving it (the possibility of same day delivery is an exciting one 
) To support card customisation with our current resources would slow things down a lot plus it would be quite tricky to scale!