Including the scriptlets from https://fedoraproject.org/wiki/Packaging:ScriptletSnippets#Icon_Cache in a package's .spec file if the package includes an icon seems redundant (almost every GUI package contains those scriptlets), is an additional burden for package maintenance and looks a bit hostile for new packagers.
Almost all other scriptlets have been converted to triggers in the appropriate packages. So, aside from ldconfig (where there is ongoing discussion about a possible implementation of triggers), the icon cache generation is almost the last thing left in fedora 25+ which requires scriptlets being present in .spec files.
This bug appears to have been reported against 'rawhide' during the Fedora 26 development cycle.
Changing version to '26'.
This problem has been solved by adding file triggers to individual icon theme packages instead. Closing.