Programming in YAML has always seemed crazy to me. Actions seem like a great place to create a simple mixed imperative/declarative scripting language (js extension or whatever) with a solid instrumented/observable/debuggable runtime and an OO API that can be run locally against mock infrastructure.
No thanks, Jenkins has three DSL languages and none of it is good. You dont have to inline code in yaml, you can call a script and call it day, write that script in any language you want.