[aerohead]

There's no way to accurately predict an outcome.
The Schl'o'rwagen experienced a drag increase upon lowering it.
The Porsche 914 experienced a drag reduction.
With the Audi A2, it made no difference.
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It's 'likely' that full-coverage wheel covers 'would' lower drag. How much would be pure speculation. Coroplast and zip-ties would tell you something.
All carmakers use MOON covers when attempting land speed records.
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If the 2023 Prius has the facility for 'one-pedal' driving, like the Tesla Model S 100D that I've driven, you'd essentially, never use the brakes, and brake cooling would not be an issue. Ergo, the non-ventilated wheel cover wouldn't necessarily jeopardize the car.
I suspect that the rotors can store the heat of a panic stop from top speed, while fully loaded, without fade or warpage.