Besides a user curated version of this, how would your phone know which apps use a lot of data? Sure, we can probably knock out youtube/Netflix/spotify, but then:
1. You really don't think Youtube/Netflix/Spotify are going to complain that Apple, by default, discourages people from using their app?
2. I'm personally uncomfortable with the idea of my phone collecting how much data I'm using per app and sending it back to Apple. Privacy is one of the reasons I buy an iPhone.
3. Setting this up leads to some very shaky experiences. How do dual sims work? What about data-only/voice only sims?
4. Bizarrely, some carriers bill traffic differently. T-Mobile, for example, bills Netflix traffic differently than other traffic.
This isn't a bad notion, but a blanket pop up actually has a ton of competing interests going into it.