Well as you know I use Linode for my provider and they have introduced object storage as well. I would just need to know if UNA would work there. Im sure tech wise its the same but just not familiar enough to know whether there are any other factors I would need to consider and then most likely the same negative of public access would be there. If that is the case then most likely adding volume storage would be the most secure solution.

We didn't add any other object storages except Amazon S3 for now, however we plan to add more storage option in the future. 

Please note that you will need to set "public" flag for existing files only, all files uploaded after switching to S3 will be properly secured.