The only time we're writing new Python 2.7 code is when we're working with Twisted (and they are vigorously migrating to Python 3). All other new code is Python 3.5 based and we're not looking back at all.

Using asyncio has been a delight for a lot of the small, quick web services we need to write (though not a replacement for Twisted). Looking forward to seeing the asyncio infrastructure grow.