Packer v.1.4.0 introduces several notable features, including support for Docker on Windows, allowing users to build Windows containers using the Docker builder. Additionally, recursive user variable interpolation has been improved, enabling more complex template definitions. A new sleep provisioner has also been added, which allows for customizable timeouts and sleep durations. Other improvements include enhancements to shell and windows-shell provisioners, updated VNC port collision detection, and integration with hashicorp/go-getter for file downloads. Notably, backwards-incompatible changes have been made to improve template coherence, but users can utilize a fixer to address these changes. The release also highlights new builders, provisioners, post-processors, and miscellaneous features such as Vault + AWS integration and updated post-processor behavior.