The beginning and end of touch events are determined with touchstart and touchend events. Wheel scrolling using trackpads on some platforms (e.g. Mac and ChromeOS) gives this information about the state of scrolling.
It might be worthy to expose this information to wheel events whenever possible:

is_first_event : false | true | Unknown
is_last_event : false | true | Unknown

* The unkown value is necessary for traditional mouse devices that doesn't provid any information about state of scrolling.

or when async wheel events flag is always enabled only the first events are cancellable:

is_cancellable : false | true | Unknown