I'd propose the followed new feature.
If in the control panel we have an opt to change manually PTR w/o droplet name is changed (add several PTR to one IP address), it will be awesome. To be more clear, if you have several ip-addresses to one droplet, maybe you need to have some reverse record to each of them.
Or, on some specific services you may need this too frequently and droplet name changing is not very convenient.
In the end, I'd like to note that it would be ok for me to have my own PTR management. I can create my own zone to rule these records. But this can be a bit dangerous for DO. If people start managing faulty records, IP-Addresses will be reported. So the best will be to add feature in control panel simply for more than one droplet's name (and this to create PTRs as users requested).