I just want to say that I strongly support either bumping the value of FD_SETSIZE to something a lot higher than 512, or making it configurable from Python code.

I am the author of a program that makes heavy use of asyncio. Some Windows users have reported errors when using big directory trees, that I could not reproduce on Linux. Then I found the note about the SelectorEventLoop limitation in the doc https://docs.python.org/3/library/asyncio-eventloops.html#windows

I can't use ProactorEventLoop because I support Python 3.4 which does not have it. I had to work around this limitation by calling run_until_complete periodically to limit the number of pending tasks. 

I sincerely think this the kind of thing that can hurt the global usage of asyncio. 
Hell I can do 600 IO tasks in parallel if I want to with concurrent.futures.ThreadPoolExecutor, why can't I do the same with asyncio?