FWIW, I agree with @lukasa that this isn't a suitable approach for a scalable system but in case I missed something I opened a ticket on SwiftNIO to discuss adding a mode where it runs in a "poll loop.
I don't think a "poll loop" is compelling because it's worse in both latency & energy efficiency than just running SwiftNIO normally on an extra thread and better at nothing that I can come up with. But maybe I'm missing something.
So if you think that a "poll loop" is indeed compelling for any use case, it'd be awesome if you could comment on the above ticket. Thank you!
Just for the record: SwiftNIO could add a mode to run in such a "poll loop" mode and then it could indeed share threads with Swift Concurrency or other systems but it doesn't seem compelling until we get Custom Executors which can solve this problem properly (and run Swift Concurrency tasks inside SwiftNIO's thread pools).