There are a number of utility functions in appstream-glib that do not exist in appstream, and without them, it'd basically impossible to migrate to libappstream.

• as-utils from appstream-glib: https://github.com/hughsie/appstream-glib/blob/master/libappstream-glib/as-utils.h
• as-utils from appstream: https://github.com/ximion/appstream/blob/master/src/as-utils.h

For example, I cannot migrate PackageKit's libappstream-glib dependency to libappstream because as_utils_install_filename() is used in the DNF backend:

https://github.com/hughsie/PackageKit/blob/ed73aa6317595d2c2f1bda7990cbd64efb133f84/backends/dnf/pk-backend-dnf.c#L524-L545