Would you consider Tornado? It's compatible with 3.x and even uses the new asyncio stuff.

I moved away from Tornado recently; I was quickly getting lost in callback hell. This was at least partially due to using libraries which did not support Tornado's method of async io natively, and a lot more fear that even putting these outputs in threads would still cause delays we could not afford.

I moved this project to Go, though I've quickly run into quirks there as well.

I'm not familiar with Tornado but I wouldn't rule it out.

I'm in the same boat, but there do seem to be alternatives which are popping up. The problem is that there is a big difference between the Twisted way of doing things (deferreds), and everything else. Once you start writing code in a twisted way it's hard to port it to anything else.

Have you considered contributing to Twisted's porting process?

Twisted is its own island.