We have just finished implementation of putio backend for rclone. Previously, it was only possible to use rclone with putio through WebDAV interface, which is read-only. Now, the new backend supports more features such as uploading, so you can do 2-way sync.
Since, Put.io does not offer free accounts we are giving away 3 months of our basic package to people who want to try putio and test rclone integration. Please send an email to firstname.lastname@example.org for invites.
putio support is coming in version 1.49.