Growth's Newcomer Homepage uses a modular dashboard setup, which allows the dashboard to display arbitrary modules, and makes development easier.
The new mentor dashboard (T239234), which is currently under development, will use the same approach. For that reason, modular dashboard setup should be generalized (most of content from BaseModule moved to a new class, DashboardModule, which will then be used by the mentor dashboard modules).
There might be some value in upstreaming this, but for now, let's do it only in GrowthExperiments for simplicity.