A very silly threshold, since this would knock out probably 95% of the app store, including games, since "websites" are extremely capable these days, with full 3d graphics, etc. Then, each time safari added a new modern browser feature, more would get knocked out.
And that little asterisk would end up getting abused by pretty much everyone. After all, we wouldn't be able to add the same functionality to the website because the developers we employ for this are only proficient in `<native language here>`.
By-intent, it would definitely be a big chunk of the apps out there, but I would argue that's a good thing. I don't want an App for every brand I interact with, especially since I know what they're doing (harvesting my data to sell to brokers to make a fraction of a penny more per transaction).