I do run M1 EP 0w-20 in my HAH. I am not one to advocate for PAO or take part in the "fake synthetic" silliness.
But I am of the mind that in a vehicle where the engine routinely starts and stops, and where the engine can turn off on a whim, while cruising down the highway at 80 MPH, or immediately turn off after ascending a long, steep hill at sustained speed, I should run an oil that ensures that there is maximum oxidation control (grp III+ is almost as good as PAO but not quite) and highest resistance to decomposition / degradation under heat soak.
The prius may or may not be as aggressive with turning the engine on and off, and may have other design elements built in. Obviously a car that makes 240k miles doesn't owe much and is OK burning a quart/1k. But if you can be proactive, its not a bad idea. Not sure Id step to a 30wt or a 5w- or 10w- oil immediately, but Id look for the stouter 0w-20 oils with lower NOACK, higher HTHS, and more intrinsic oxidation resistance.