The point here is that implementing new features will be impossible, because this relies on an existing implementation that is not in python.
It is therefore not a proof that arbitrary high performance applications can easily be written in python.
It is simply an example of how high performance applications based on existing implementations someone else had written in another language can be wrapped in python.
Isn't that the opposite? Implementing new features will be easier, because it uses the C backend a helper library (for parsing, eventing), so all the business logic is Python which is easier to extend.
This is also why people use embedded Python/Luc/etc in games, 3D programs, and so on.
And in many cases you're the higher up, and startup founders take decisions to use slower but more flexible technologies every day...