[aarmenaa]

If you manage to avoid scope creep then sure, static YAML has advantages. But that's not usually what happens, is it? The minute you allow users to execute an outside program -- which is strictly necessary for a CI/CD system -- you've already lost. But even if we ignore that, the number of features always grows over time: you add variables so certain elements can be re-used, then you add loops and conditionals because some things need to happen multiple times, and then you add the ability to do math, string manipulation is always useful, and so on. Before you know it you're trying to solve the halting problem because your "declarative markup" is a poorly specified turing-complete language that just happens to use a YAML parser as a tokenizer. This bespoke language will be strictly worse than Python in every way.

My argument is that we should acknowledge that any CI/CD system intended for wide usage will eventually arrive here, and it's better that we go into that intentionally rather than accidentally.