The problem is the usual with a federated protocol: adding a feature requires you to extend all the clients, which does not happen. See for example PGP.
The features are completely opt-in. If you don't want to link your email to your schedules or TODO list, you don't need to do anything. The same information should be present in a human-readable format in the body of the email anyway. (YAML might be better than JSON for this purpose.)
