Those are alerts though, not circuit breakers. (Although alerts can be used to trigger certain types of circuit breakers.)

What some people are asking for--and it's a reasonable use case but one that AWS, somewhat understandably, isn't really focused on--is: "Burn it all down if you have to, including deleting databases, but no way no how charge me a penny more than $100/month (or whatever my set limit is)."

The circuitbreaker everyone would want is probably: "Drop all compute with its ephemeral storage, when the cost of every resource already used and the projected cost of my stable storage (EBS+S3+Glacier+Aurora+Whatnot) is greater than my preset $MONTHLY_MAXIMUM.

That means any data getting lost as a result of that limit is data that they weren't guaranteeing in the first place. You might not be able to actually read your EBS volumes, S3 buckets or Aurora tables without increasing the spending limit or otherwise committing more funds, but it won't go away that second, and you would have enough time to fix it (worst case - wait until next month; you did budget that already).

Alternatively: assign each resource to a pool, and monthly spending limits to each pool. Give your EBS/S3 $1000/month, and your R&D-pet-project-that-may-accidentally-spawn-a-billion-machines $50/month.

Projected cost of persistent storage is still tricky. But, yeah, something along the lines of "Turn off ongoing activity and you have to true up persistent storage soon or it goes away." I don't think one would actually implement a system where a circuit breaker immediately and irrevocably deletes all persistent storage.

And, as you say, it makes sense to have a pool--whether it's your whole AWS account or not--where you can turn on the "burn it all down" option if you want to.