Honestly, I'm leaning the opposite direction — we may want to remove some of the implicit cancellation checks that are already there, e.g. so that Handle.get() always reports the task's true result. Making await always check and throw on cancellation would make it extremely frustrating to write a task that can limp through and finish its work despite cancellation, which is sometimes quite useful.
EDIT: although maybe those use cases aren't a good fit for cancellation.