More a request than an issue, but would it be too complex to implement a "move your /48" from one tunnel to another? I understand the /64 pool at certain endpoints but whoever asked and is actually using a /48 as a /48 most likely has a good number of systems using these subnets and it might not be an easy change to get them all updated (talking static assignments, interfaces, security policies, domain entries, etc) to the new assigned subnet. However, trivial to change just your endpoint tunnel setup.
Happy for your consideration, and really appreciative for your services: years ahead of what our paid ISPs offers (which for my sad VZ case, is just non-existent).
/48s are also allocated from a server-specific pool. Making them portable would also result in tens of thousands of additional routing entries.