Currently, the Schema namespace is validated by Extension:EventLogging, using a custom-written JSON validator, and a custom schema. The EventLogging server uses a stock JSON schema draft 3, however. This means that some documents which pass initial validation and can be stored as an EventLogging schema will crash the server in a way that sends alerts, and drops hours of data at a time.
We can improve this situation by replacing the MediaWiki extension validator with plain JSON-schema draft 3.
Update: Validation at both ends should use a "allOf" to enforce both JSON draft 3 as the base schema, and additional restrictions matching the new guidelines for Wikimedia EventLogging. Write a legacy schema to allow e.g. camelCase fields, and a strict schema for conforming newer schemas. The stricter schema can be introduced gradually, e.g. by "oneOf" and something like MediaWiki extension registration's "manifest_version" as a mandatory field when using the newer contract.