One thing they're not great for though is shareability. With gifs, you can generally just drag & drop them between most apps and they'll behave as you expect. Not true with videos.
I can sort of comment on this since I've used Flask-RESTful and Django REST Framework where a lot of the Flask-API design is/will be borrowed from. I think the browsable API feature is great but it's not the killer feature for me. To me the killer feature is the well-designed serialization and validation architecture. In Flask-RESTful this seems half-baked - there is no notion of hyperlinked references or nested objects. At our company we ended up implementing our own serialization & validation layer which felt a lot like reinventing the wheel. My hope is that we can bring this same great architecture over from DRF to Flask-API.
We've been considering "porting" our app from Flask-RESTful to Django REST Framework because it is so well architected, tested, and has a large community around it. So I'm overjoyed to hear that you're bringing this awesomeness to the Flask world Tom!
Most welcome! For anyone on this thread who's interested in contributing I'd suggest opening a ticket citing your interest, so that we've then go a place we can start the discussion from.