I'm not saying there's no reason for double-drop-d. Of course there's good reason for the tuning. Just not much reason for a chord chart.

The need for a chord chart implies that one would already know what chord they want to know the fingering for. If one already knows what chord they want to play, they can VERY easily figure out how to do it in double-drop-d. They can do so because double-drop-d is essentially a standard tuning. It is merely a minor alteration from a standard tuning, rather than an open altogether-alternate tuning.

What chord could you know that you want to play that you couldn't easily figure out in double-drop-d?