For the record, digitalocean now supports this and we are open to extending core to allow for “any” s3 compatible location. Just need to figure out how this would be entered via site settings.
I guess you would select “custom” in the s3 location and then add a custom_s3_url or something like that.
#pr-welcome for this but I do want full details about the site setting changes to be made prior to implementing anything.