Here is the latest I received from Shopify:
Hey Kevin,
Azhar from Shopify Support here, hope you have been well today.
Just quickly reaching out regarding our conversation from earlier, I’ve just heard back from that technical team regarding your request to get additional information on whether you would be able to merge customers in the future.
The technical team specified that there are currently no public facing documents regarding this request, resultantly we would not be able to divulge any information on when exactly this feature may be introduced. However, we were both able to notice that it is indeed a common request by other merchants, and resultantly it is extremely likely that the design team is looking to implement this in the future.
I know this may not have been the exact answer you were looking for, however currently this is all the information we are able to provide regarding this.