The quality of integrations labeled internal quality vary considerably. If they were reviewed the way new integrations are they might get labeled bronze or rejected. Some have long standing bugs (Threshold, History Stats)
Ideally internal integrations, particularly those that provide helpers should also be reviewed and rated under the same scale that new integrations are required to.
The internal tier is assigned to integrations used internally by Home Assistant. These integrations provide basic components and building blocks for the Home Assistant Core program or for other integrations to build on top of it.
Internal integrations are maintained by the Home Assistant project and subjected to strict architectural design procedures.
Characteristics:
Internal, built-in building blocks of the Home Assistant Core program.
Provides building blocks for other integrations to use and build on top of.
Maintained by the Home Assistant project.
I’m not sure that the examples Threshold, History Stats meet the requirements for internal integrations.