> You know what version of your pipeline built the software at any point in its history.

Source control can tell you when changes to the pipeline were checked in, but they actually take effect when they're applied with 'fly set-pipeline'. That may be before or after they were checked in. Perhaps a sensible team would set up a pipeline to watch the pipeline repository for changes and apply them automatically. Mine hasn't.

> Concourse boils the unit of extension down to "resources"

Which you can only actually use by forking the Concourse BOSH release to add them to the workers [1]. I'm not sure i'd honestly call it a point of extension.

[1] https://github.com/concourse/concourse/blob/master/jobs/grou...