In the spec, the non-reversible form of Variant is described using language like this:

For the non-reversible form, Variant values shall be encoded as a JSON object containing only
the value of the Body field.

The problem is that "JSON object" means something very specific, both in the context of JSON itself, and the way that phrase is used in the rest of the spec when it talks about encoding an object. As written it implies a Variant (containing e.g. true) in the non-reversible form would be encoded like:

{"Body":true}
or
{"SomeField":{"Body":true}}

Speaking with Randy, the intention is that it would simply be:

true
or
{"SomeField":true}

He suggested the spec should say:

For the non-reversible form, Variant values shall be encoded as a JSON value which is the same as the value of the Body field.

ExtensionObject is also described using this language and I suspect the actual intention is the same as Variant.