At the Wikimedia Tech Conference 2019, the topic of global templates was discussed in two sessions (T234661, T238251). One topic that was repeated several times is the need for a dependency tracking tool for modules and templates, that would work globally when needed. One of the proposed solutions is to adapt the GlobalUsage extension to this.

This task is just an initial exploration and post-conference documentation. One immediate issue I can think of is that it's a bit of a chicken and egg problem—what to do first: adapt GlobalUsage or make modules global? But I guess it can be resolved.

See also:

• T253026: Introduce a centralized Dependency Tracking Service
• T370378: Explore usage tracking for chart pages and tabular data pages