For a lot of the personal projects and early stage startups that are most terrified of these kinds of mistakes and therefore avoid autoscaling products like fly.io, we sincerely would rather have the entire account shut down when it goes over budget than ever see a bill that's higher than our net worth. A line item veto somewhat alleviates that concern but not fully.
They indicate at the end that they're going to do something along these lines, but what they're describing there also seems over-engineered compared to a simple circuit breaker that kills the account or some subset of it. Is there a good reason for these providers to avoid implementing that feature, which on a naive look seems far simpler than what they've actually proposed?