Is it possible to get a fully typed Scalar Union

[lemiesz]

So my application I need to render a list of items, the list is user defined, and user can mix and match item types as much as they want. Basically its a list of activities that are sequenced by a content creator and show to a user.

Example

items: [
  {
    type: "ACTIVITY", 
    ....
  }, 
  {
    type: "VIDEO_ACTIVITY", 
    ...
  }, 
  {
   type: "CUSTOM_INTERACTION", 
   ...
  }
] 

These are stored on back-end service that my GQL service interfaces with. The Backend service just stores this as Stringified JSON.

On my GQL service I am just using a simple scalar to parse that string for the use.

new GraphQLScalarType({
    name: 'ItemDataStructure',
    serialize: (value: any) => {
        return JSON.parse(value);
    }, 

However I already have the types and parsing logic for these different item defined in a common rendering library. I would like to write a scalar that parses these items, and returns a fully resolved type to the front end.

is this possible with Graphql? I know there was some discussion a while back about adding Scalar Unions... does any one if that was resolved? If not is there a way to make my usecase work?