That's a good idea. I think a lot of people have that trepidation about switching to flask. Just a quick "instead of this in django, use this in flask" section would go a long way.

I think there's a great book to be written about scaling codebases that started out as monolithic MVC frameworks (Django, Rails, Struts, etc.) I find Flask's design is heavily informed by the problems that monolithic frameworks create, so it would be a great case study, but it's totally out of scope for an intro to flask, though.

I wonder if "Flask for recovering Djangonauts" would make for a good blog post / tutorial. It might even be enough material for a video course. Best practices, advice, and good libraries are what I'm shooting for with Explore Flask, so hopefully that will come across.

As far as official library integration goes, I wouldn't worry about it too much. There are several standard extensions that people use (e.g. Flask-WTF, Flask-Bcrypt, Flask-SQLAlchemy) and as long as you stick with them you'll be alright. They're usually just wrappers around major Python libraries (WTForms, Bcrypt, SQLAlchemy) so the source is easy enough to check out.