JSON schema is a much more complete language for validation. And every types in the limited TJSON can be described with JSON Schema.

Besides that, in JSON Schema the schema is not bundled with the data. This is a feature for input validation: the receiver must know what it allows, not just what is received. This is a feature for readability (which is a great feature of JSON) as the data is not uncumbered with the schema. A receiver is free to use a schema or not. While TJSON imposes a receiver to recognize its dirty format.

So TJSON brings nothing new, except interoperability problems.