Absolutely not. That practice should literally be illegal.
> or do they have to drop them randomly?
Yes. This is the only reasonable approach.
> And can you pay to be in a “never drop my packets” group?
No. That should be illegal to offer.
If the ISP's network is incapable of meeting their customer's demands during peak hours and they oversubscribed themselves so badly that they're contemplating such tactics then they ran their business dishonestly. They fraudulently made promises that they were incapable of delivering on and got caught. They need to fix their network or go out of business. And possibly should face legal consequences for their behavior.