In my opinion this is a really big oversite with Enhance. It can be managed with a custom script via the API but a panel should support HARD limits with auto suspension and warnings for upselling.
Bandwidth
Excessive sustatined throughput .
Disk space
Excessive disk IOPS
Memory usage
CPU usage
I think all of these should be configurable to send notices to admin, webhook, and/or customer based on defined levels. In this way, each company can customize it as they see fit for their business. I say webhook so that integration is easy via zapier or billing software.
For example
Webhook/Email - 1gb bandwidth overage
Suspend - 10gb bandwidth overage
Webhook/Email - 5% remaining disk space
For sustained type usage maybe a setting like x% usage average over y time. Ie 90% memory used in last 24 hours.