It seems like this problem is solved by simply setting a sensible minimum in an autoscaling group. And not "everyone on Earth was abducted by aliens and stopped using the service" levels of minimum.

Say I'm an e-commerce site and on Black Friday I can see historically (or just make an educated guess if it's your first holiday sale) I get "n" requests per second to my service.

I'll set my autoscaling group the day before to be able to handle that "n" number of requests, with the ability to grow if my expectations are exceeded. If my expectations are not met, then my autoscaling group won't shrink. Then the day after the holiday sale, I can configure my autoscaling group to have a different minimum.

This solves the problem of balancing between capacity planning and saving money by not having idle resources running.

If you're the type of person who hates human intervention for running your operation, then fine. Put in a scheduled config change every year before a sale to change your autoscaling group size.

It's pretty rare to have enormous spikes in application usage without good reason. Such as video-game releases, holiday sales, startup openings, viral social media campaigns.