Earlier quoted context omitted.
It's difficult to come up with a good model for how a billing ceiling would work in software as a service. A good start would be to fully specify what behavior you desire when an account hits its billing limit. Are you expecting everything to keep working like normal while the cloud provider pays the bill for those resources, or are you expecting the provider to fully shut everything down in a way that prevents the a…
"it's reasonable for cloud providers to give billing threshold alerts while leaving the choice of what to do in the hands of the customer.". But, they don't don't give us the choice. I need to keep an eye every moment of every day for an alarm, as hundreds or thousands of dollars rack up. That's the ONE THING I DON'T WANT. I'd take anything else (delete my data, lock everything, whatever) over charging me money I can…
You know you can make a machine do that for you - right?
In fact all the tools Amazon would use to do this are available to you right now. Cloudwatch, SNS, and Lambda are 98% likely to be all you need - apart from the time to get it set up to do whatever you think is "the right thing".