Even before task groups land, this API can be easily improved by adding

asyncio.run_in_executor(func, *args, **kwargs)

- Only valid inside a coro or async context (uses get_running_loop internally)
- Analogous to how `loop.create_task` became `asyncio.create_task`
- Drop having to specify `None` for the default executor
- Users already know the `run_in_executor` name
- Allow both positional and kwargs (we can partial internally before calling loop.run_in_executor)