As of Fusion Server 4.0, connector plugins can be hosted within Fusion, or can run remotely. The communication of messages between Fusion and a remote Connector or hosted Connector are identical; Fusion sees them as the same kind of Connector. This means you can implement a plugin locally, connect to a remote Fusion for initial testing, and when done, upload the same artifact into Fusion, so Fusion can host it for you.
The connectors architecture was designed to be scalable. Depending on the connector, jobs can now be scaled by adding new instances of the connector. The fetching process for these new types also supports distributed fetching, so that many instances can contribute to the same job.