Re configuration files: an experimental implementation is now in the development version (described here) and the plan is to send it to CRAN next week. @noamross, when I responded to you earlier, I assumed that a configuration file would require changing existing drake functions and going against the design philosophy. I no longer believe that to be the case, I think we can have the best of both worlds.
The new experimental callr-like API does not change drake's modern/tidy worldview, but it does make it more amenable to file-based workflows. The pipe, if we decide to merge it, can coexist.