I especially love the library management part. There's no versioning, but it's really helpful to be able to just list your libraries and have them be automatically downloaded and linked to your executable.
It is! :)
http://docs.platformio.org/en/latest/librarymanager/index.ht...
Please note that you can manually update manifest and make PR to author's repository. Click on "Manifest" tab when looking at a library in Web Registry and you will see "Edit" button.