Say I keep my containers as light weight as possible, perhaps using alpine or some other light weight distro.

When something goes wrong in a pod, it can be difficult to exec in and debug sometimes because there are no debugging tools in the container.

It would be awesome if you could temporarily attach a new sidecar container to the specified pod for debugging purposes.

something like:
kubectl exec -it mypod -s mydebugcont /bin/bash

It could even perhaps take a -c flag and attach to the same pid namespace of the specified container so stuff like running strace -p would work.