Ability to remove Enumerated List Item definitions without need for removal of value from Attribute against individual Artifacts

We've need to remove several Items from within Attribute Data Type Enumerated Lists of Items (Enum), within the Type System.

We've recently discovered, if the Item so removed were applied as an Attribute value to an Artifact Object when the Item was defined (e.g. Requirement Artifact Type), when displayed, the values of the Attribute for the Artifact will appear as an omission to the list of values (i.e. the Requirement Artifact retains knowledge that its Attribute has the value no longer defined within the Type System, treating it as undefined).
E.g. Requirement Object 123, has Attribute: Applicability: ABC, DEF, JJJ
If I remove the Item of Label: ABC from Attribute Data Type: Applicability, Requirement Object 123 will show the following Applicability: " , DEF, JJJ" (note the 1st comma and value missing just prior).

This however is but an indicator as the downstream implications are far more significant. Because ABC is no longer defined, Requirement Object 123 can no longer be imported/migrated as it returns an error message stating the Item is undefined (referred to by DNG internal URI).
We need a solution that doesn't require the value's removal from the Attribute on 4.9M+ Artifacts (x 5+ variant Streams) before removing the Enum Item as this is untenable.

In addition to foreseeably needing to do so periodically as a matter of course, we've an acutely significant need as we've encountered the practical upper limit for the number of Items defined within an Enum for one of our most active Attributes.*

NOTE: While this is written within the context of DNG, this need exists in the other major ELM Applications of EWM and ETM.

*I'm aware there is no technical hard stop, however, there is a practical limit, after which, any attempt to make updates to the Enum list will result in fail by timeout (especially as ours is a Classified environment with all the performance limitations one would expect from highly regulated/controlled infrastructure)…

NOTE: Removing an Artifact Attribute from an Artifact Type when the Attribute has values assigned to it by instantiations of the Artifact Type doesn't seem to cause any issue, surely there is a means for a similarly practical solution.