For a long time there have been efforts to ensure at least a degree of quality and robustness through processes, practices and verification tools. One such tool is a type system which allows encoding requirements and expectations that will be automatically verified with the help of a checker. This is exactly what Instagram is attempting in an effort to increase quality and ease maintenance.
It seems many are wondering why they haven't done this from the beginning. A typical (and probably correct) answer is development speed and flexibility: early stage companies need to be nimble and compromise on quality if they want to survive. Fair enough, I understand that. We can applaud Instagram's success on the markets, but that doesn't have to mean that they're a role model of technical excellence for building a million line Python code base.
This tool is the proof that Python has significant problems at scale, which is something the Python community has denied for a long time. They're still doing it in this thread, but the lesson looks pretty clear to me: if you plan on building large scale, don't use Python. Or PHP while we're at it (see Facebook). Definitely not JavaScript (see FirefoxOS).
The founders of a start-up can continue to do whatever they want in the name of success. Instagram at their beginnings was basically a different company from today's Instagram, no one would have used them as a technical role-model. Now they're at best a role model for large Python code bases, but many here seem to be drawing the wrong conclusion, namely that it's a good idea to do large-scale Python in the first place.