Which feature do you think can be improved?

Docs. Annotations are available to be used (see annotations.go) but not documented.

How can it be improved?

By adding an Annotations.md file and linking to it from whereever applicable.

Additional Information

Maybe also create use-cases based on annotations (e.g. custom rootfs #294 )

Before raising this feature request

Have you looked at the limitations document?
Yeah, I doubt if it applies to this document.