Support GraphQL `oneOf` input directives in AppSync?

Are there any current plans to support the new [GraphQL `oneOf` directives](https://github.com/graphql/graphql-spec/pull/825) for input objects in AppSync?

Some other GraphQL libraries are starting to roll out support for these, e.g. [support appears to be implemented in Apollo's kotlin client](https://github.com/apollographql/apollo-kotlin/issues/5431). They're very useful for typing queries where inputs have mutually-exclusive and/or dependently-required optional properties, since union types are not and it seems [will not be](https://github.com/graphql/graphql-spec/issues/627) supported for inputs.

It looks like there's something of a consensus forming around `oneOf`, so it'd be great to have an issue we can follow regarding support in AppSync.

No repository files, tests, or implementation entry points are identified. Start by reading the linked GraphQL oneOf proposal and comparing it with AppSync's current input-object support; done would require an accepted implementation scope or a documented AppSync support decision.

Written by the indexing model from the issue text.