[gngeal]

"While async/await is a cool feature and is worth using, it is worth noting the up trend in complexity of generated code – and ansyc/await generates significantly more code in the simpler language without this feature than previous new features did."

This is the case with all high-level language features. Full lexical scoping with first class functions forces the PL implementation to either generate a <code;environment> tuple for all function values, or to perform aggressive closure conversion (up to Stalin levels) in addition. Virtual method dispatch gives rise to inline caches, often polymorphic ones. Lazy evaluation forces you to generate thunks. Pattern matching forces you to generate a decision tree or a similar structure. The list goes on. You already have such things in C#, even without async calls.