The issue is not clear.

The Variant definition says:
If the value is a scalar, it is encoded using the rules for type specified for the Type.

For the reversible it would be encoded as a number.
So for non-reversible the variant would be the non-reversible encoding of the enumeration or a simple string.

There is no inconsistency with XML because XML does not have a non-reversible encoding.
The JSON and XML rules for reversible encoding are the same.

1. From the common description it looks like Enumeration is not directly supported in a Variant (neither listed as built-in type nor an ExtensionObject).
   Binary and XML describe that Enumerations in Variants are encoded as Int32.
   In these cases I interprete it like "store the enumeration as Int32 in the variant and encode it".
   There is no such extra statement how to encode an Enumeration inside a Variant for JSON or I did not find any.

The problem is that our SDK is currently not able to store the full information of an Enumeration value (type name, value name and number) inside our variant data structure to select the representation via the JSON reversible flag.
Once stored as Int32 it is always encoded as Int32.

2. A Variant for reversible has to encode the used built-in type in the "Type" field but JSON number is not a UA built-in data type.
   We need to know which type ID to encode here even though the "Body" is the same.
   The related built-in type Int32 is specific for Binary and XML but not described for JSON.
   This obviously does not matter for non-reversible as the Variant "Type" field is omitted.

Added text:

If an enumeration is encoded using in the reversible encoding within a Variant, the Type field is Built-in Type Int32.

Agreed to changes edited in Web meeting.