@deadsuperhero I think there is an easier way. Implementations can generate fallback representations from the standard content property and ignore the object type. I.e. we treat content property as a lowest common denominator.
Optionally, use name or summary if content is absent. This is what I'm currently doing and it works reasonably well.
Relevant Mastodon issue: https://github.com/mastodon/mastodon/issues/24079 (upvote, spread the word, etc)