Duplicate Module?

Although your right that Amazon S3 is often enabled on Swift it's still optional and not necessarily available. The S3 implementation in Storage API has the Amazon url's hardcoded in the code and is unusable for now:
services/s3.inc:124

   $ch = curl_init(url('http://' . $bucket . 's3.amazonaws.com' . drupal_encode_path($object_name), 
      array('query' => $query)));

services/s3.inc:244

    $ch = curl_init('https://cloudfront.amazonaws.com' . $path);

Also I miss a important feature which allows you to override the public:// and private:// streams with the storage container.

It would be a good option to integrate native Swift API as a backend in Storage API though and I did not know about the module when I created it (just searched for openstack and swift). At this moment the Storage API did not receive any updates for 11 months. The Rackspace Cloud library it recommends when installing doesn't even exist anymore. So I would choose to develop this backend further and integrate it in Storage API with a patch if it gets active again.

Adding and linking modules to issue description.

FWIW, Storage API seems to be under active development at present.