> The change is slightly not backward compatible but

Yeah, that's my main problem with converting `loop.run_in_executor()` to a coroutine. When I attempted doing that I discovered that there's code that expects the method to return a Future, and so expects it have the `cancel()` method.

If we convert it to a coroutine a lot of code will break, which might be OK if it's really necessary. Is it though? Can we return a special Future subclass that complains if it's not awaited?  Would that fix the problem?