Thanks for the interesting links - I'll check them out! We would need not just another CI but also another container platform because launching a docker container is also slow.

Irrespective of the CI, I believe all cached Docker layers will need to be downloaded onto the build machine before it can be rebuilt.

Still, I believe it is possible to build and deploy faster even with a "docker image only" design and it's something we are still looking at. The question is what is the lower bound here - would be hard to beat "sync a file to a warm container and run it". Pex gives us a pretty good lower bound that is also container platform agnostic.