There are still a lot of Django apps that work fine in this scenario. Plus I don't think the slides imply that they are just blindly replacing ORM calls with raw SQL, just that they have profiled and replaced the hot spots.

Also Flask is a micro-framework and Django is a full-stack framework. Flask can be used as the backbone of a full-stack framework but figuring out a good project structure and finding out what third-party apps to use can be daunting for a person without Flask experience. If you really want to get people to switch, package up a Flask-based framework with the features of Django.