> but I'd say the issue with C++ coroutines (and 'colored' async functions in general) is that the whole call stack must be written to support that.

You can call a function that makes use of coroutines without worrying about it. That's the core intent of the design.

That is, if you currently use some blocking socket library, we could replace the implementation of that with coroutine based sockets, and everything should still work without other code changes.