For a table that has a subtype:

The subtype fields have domains.
For example, when the ASSET_CLASS subtype value = 0 (ACTIVE_TRANSPORTATION), the ACTIVITY field uses the ACTIVITY_ATN domain.
Problem:
Just like with regular domains, subtype domains can be easily overridden via the Field Calculator and other mechanisms.
For example, 'asdf' is not a valid ACTIVITY_ATN domain code, but I can still enter that value via the Field Calculator.

Idea:
In ArcGIS, hard-enforcing subtypes and domains isn't supported, and likely won't be supported any time soon.
As a workaround, could Esri provide a sample attribute rule for enforcing subtype domains? (in the Esri Arcade GitHub)
Thanks.