Indeed, tornado and pyftpdlib implementations are much more complex,
have somewhat different APIs (i.e. only support FDs), have special
cases for older python versions, lack some newer features (e.g.
context manager).
The current code is much close to Tulip's.

> Exploring this into Tulip would be important IMO, as it would help figuring out whether the API is good enough to support what this component aims to achieve: being a generic poller upon which to build async IO loops.

That's indeed a good idea, there's no need to rush this in.