The problem that compounds there is that the icon theme directory is not writable, so they can't be added the standard icon cache. We'd have to define a new icon cache that was built from the icons in click packages. Not impossible.
I think that probably a better solution for components that need to use icons in click packages to install click hooks that are appropriate for the icons they're interested in so they can build a cache of what they need. A generic cache here doesn't seem as useful when we can adequately detect changes on a per-component basis and evaluate fallbacks at package install time instead of runtime.
The problem that compounds there is that the icon theme directory is not writable, so they can't be added the standard icon cache. We'd have to define a new icon cache that was built from the icons in click packages. Not impossible.
I think that probably a better solution for components that need to use icons in click packages to install click hooks that are appropriate for the icons they're interested in so they can build a cache of what they need. A generic cache here doesn't seem as useful when we can adequately detect changes on a per-component basis and evaluate fallbacks at package install time instead of runtime.