A private blockchain is an oxymoron. The point of a blockchain (as it's understood by the crypto world, at least) is for it to be publically readable by anyone.

A private blockchain is just a database.

The problem with your idea is that when designing a programming language you are creating something meant to be replicable. If you obscure part of the language within a black box, you nullify the entire purpose of creating it in the first place. Is your goal to create an unanalyzable-by-AI programming language or is it information security?

… what is the goal here? What’s the reason you want a programming language that LLMs can’t learn?