Recently I've been having conversations with various relevant people about creating [[ https://www.mediawiki.org/wiki/Global_templates | global templates and modules ]]. One proposal that came up from @daniel is to make a way to import a module that resides on a global wiki from a module that resides on a local wiki without allowing the invocation of a global module directly from a wiki page.
According to @daniel, this can be done without making a full implementation of general change propagation and dependency engine mechanisms. It will also create a feature that will be needed in any case for at least some global modules: version management, that is, making sure that a particular version of a module is used on a local wiki (it is needed for sensitive modules, upgrading which can break wikis).
This will not create a full implementation of global modules because it will require doing //something//, even if it is something easy on every wiki that wants to use a global module, and the whole point of global modules is that they will be immediately usable everywhere, like Commons images. This still will have to be done (T14610). Nevertheless, the importing from a global repository is a useful and probably necessary step in the right direction.