The problem of the main thread waiting on a response from the database is easily solved without rewriting all your code, which incidentally will have the same issues, since there's no new magic there.
If your software is a giant, ugly hairball because you wrote it in a hurry (I know I did this many times!) don't blame it on the language or framework. What I'm wondering is: Python/Twisted/Django rank equally or similarly on all the points from the list, except for Team Experience, which has to be much higher with the old stack than with a completely new technology and set of tools. This makes me think that there was a "play with shiny things" point after all.
Python has no such conventions, making many libraries into dangerous minefields for the Twisted developer.
I'm personally not a huge fan of node, and I prefer to write non-blocking code in Aleph/Netty (which is closer to twisted in terms of potential to block due to blocking java libs) myself.
But, I can understand on a large team not wanting to deal with the potential for blocking libs.
That said, if performance is that important, it should be part of your test suite, and should catch that.