> Regularly calling executor.shutdown() and then instantiating a new ThreadPoolExecutor in order to run an asyncio program does not seem like a good API to me.

Clarification: you're typically only supposed to instantiate a single ThreadPoolExecutor or ProcessPoolExecutor per program (sometimes one of each depending on use case), and continuously submit jobs to it rather than creating multiple executor instances. Otherwise, it's generally unneeded overhead.

(I'll take a look at the other parts once I find the time, just wanted to briefly mention the above in the meantime.)