Operate directly on ASTs? An optimal language that is "hard" for humans to use (hardly), but a good fit for LLMs? No need to reinvent the wheel (endlessly). These guys have been at it and carrying the flag for a very long time now (they're probably pretty exhausted):
A Programmable Programming Language
https://cacm.acm.org/research/a-programmable-programming-lan...
See also:
What is a programmable programming language?
https://hiphish.github.io/blog/2019/06/22/what-is-a-programm...