We used Python 2.7 for pypy compatibility. I really dig the new async/await primitives added to Python 3.5 and think the asyncio path is the best path forward. I hope the work to get all the latest asyncio stuff working on PyPy picks up some steam.
if Pypy + asyncio was available, would you have built everything using that stack ? There have been all these benchmarks that asyncio is so much slower than threads [1] How would you compare that with Go ?
[1] http://techspot.zzzeek.org/2015/02/15/asynchronous-python-an...