S3a now supports different regions, by way of declaring the endpoint —but you can't do things like read in one region, write back in another (e.g. a distcp backup), because only one region can be specified in a configuration.
If s3a supported region declaration in the URL, e.g. s3a://b1.frankfurt s3a://b2.seol , then this would be possible.
Swift does this with a full filesystem binding/config: endpoints, username, etc, in the XML file. Would we need to do that much? It'd be simpler initially to use a domain suffix of a URL to set the region of a bucket from the domain and have the aws library sort the details out itself, maybe with some config options for working with non-AWS infra