Based in a table, KEY-VALUE, we could expand the ENUM field from limited size (65535 values) to a unlimited size (64bits), this is a new field type

ENUM_EXTERNAL(database,table,key column,value column)

the internal value of ENUM_EXTERNAL is a bigint, the string representation is a blob (or maybe a varchar(255) or a text)

the point is:

the storage engine will save a bitint
the mysql core will convert the STRING to BIGINT using the database/table/key column/value, using a SELECT like this:

SELECT <value_column> FROM <database>.<table> WHERE <value_column>="FIELD VALUE SEND VIA INSERT/UPDATE/DELETE"
UNION
SELECT <key_column> FROM <database>.<table> WHERE <key_column>="FIELD VALUE SEND VIA INSERT/UPDATE/DELETE"
LIMIT 1

this solve the problem of .FRM file don't allowing a big definition of ENUM/SET, and add an feature to developer of an avoid of alter table to change enum definition (it can use the external table to define the key-values of enum)