This would require that any new image format only did things that were foreseen by the creators of the metalanguage. If the metalanguage is Turing complete the

This would require that any new image format only did things that were foreseen by the creators of the metalanguage. If the metalanguage is Turing complete then it's just an interpreter. Python, for example, could be your metalanguage. Then I would argue that we already have this.