It is misguiding to say that boto supports Python 3. The boto3 repository (https://github.com/boto/boto3) is experimental and far from feature completion. I am even not sure if it's API compatible with boto. Further, it has been dormant for quite some time.
boto3: https://github.com/boto/boto3/tree/develop/boto3
boto: https://github.com/boto/boto/tree/develop/boto
It don't understand why python3wos changed its status.