I searched for answer to this question, but didn't come across a topic that seems to have directly addressed it. Hence I am posting it as a new question.
From this Google App Engine page, it says that webapp2 is a lightweight framework that allows you build simple web applications for the Python 2.7 runtime.
The emphasis above seems to be on simple web applications. Given this I wonder if it hints at webapp2 python framework not being suitable for large scale complex applications that need to scale to several million users. What is the reason that it wouldn't scale (because I thought Google App Engine is a platform designed to scale regardless of what language or framework one uses).
I am trying to make a decision of whether to use the webapp2 python framework (easier to learn and get going) for my website that might potentially have to scale to the millions of users or if I should consider other frameworks.
webapp2 is unfortunately not actively developed and maintained. I have been using it for simple web apps that have around 100 users a day - and I have not witnessed any performance drops.
Scalability is not only about the framework, but the quality of your code, database design, queries, servers etc. Google App Engine provides the resources (bandwidth, space, processing power) but it does not write the code for you. GAE helps you scale when you need it and on the go.
https://code.google.com/p/webapp-improved/ - check the issues page, you will see a lot of unsolved issues and the project seems abandoned. As a developer why would you choose a project that is abandoned and does not have an active community?
If you want to stick to python I'd refer you to this question: Does Django scale?
Hopefully that will provide you with enough information to answer your question.