We need / should implement an expert in ValueView for UnDeserializable value.
what I came up with is:
where it displays the error and users can remove the value. (they still need to look at something like Special:EntityData to see the raw data, if they like. in the future we might be able to add some "details" display of the raw value or make more attempt to try to reparse the value)
for now, I want something simple that works sufficiently. (vs. totally broken as is the current situation)