MediaUploader registers which templates are used in campaign configs and this allows for campaign config cache invalidation every time a transcluded template is changed (through the LinksUpdate mechanism). This currently does not work for the main global config.

The best I've come up with so far:

1. Define a new content type, let's call it MediaUploaderConfig, for a single "magic" page, maybe in a special-purpose namespace.
   1. It seems that defining an entire new content type won't be needed, we can hook into an existing one, using this hook.
   2. We probably could try to hack around and make the page impossible to delete, but I'm not sure if it will matter at all. More investigation needed.
2. Whenever we detect a global config cache invalidation is necessary, we also enqueue a LinksUpdate for the magic page.
3. Have the content type override getParserOutput() and similarly to CampaignContent, use the GlobalParsedConfig::getTemplates() method to register all used templates on the page in the ParserOutput object. This will cause a LinksUpdate for this page whenever any of the transcluded templates are changed.

Drawbacks: complicated and hacky. On the other hand, it mostly uses built-in mechanisms.