There are a lot of different plastics, absolutely, with different fillers for reinforcement. Plastic doesn't simply mean it's made out of recycled milk jugs.
But this is an application with cold temperatures (where plastics get more brittle), and sudden impact loads. I work with plastics at work, but this is not an application where they'd be my first choice.
My Toro 1800 single-stage electric has a plastic paddle. It works fine, and fortunately I've never had one break. They do show signs of wear, with grooves and notches in them, but they've held up. But I use it for the deck, which doesn't get chunks of ice like EOD.
I think the earlier comparison was fair. If you hit something solid enough that it bends a metal impeller, the odds are decent that it might crack a plastic impeller.
The plastic chute in my MTD worked well, no complaints. But I would not be comfortable with a plastic impeller, personally. If they turn out to be robust, and still running strong after 20 years, that will be great, and I'm happy to be wrong. But I'd rather not have one on my machine.
As just a single reason for that opinion, if a metal piece on my machine cracks, I can weld it. But if a plastic impeller cracks, the best I could do is drill a hole at the end of the crack, and hope it doesn't continue to grow.
I don't think lighter weight of the impeller offers the machine a big benefit. The bearing still takes most of its load from the snow being flung, rather than from the weight of the impeller. A plastic impeller *can* probably have tighter tolerances for concentricity of the blade tips, allowing a smaller gap to the impeller housing. But the impeller housing is the other half of that discussion, so I'm not convinced you'll suddenly see a nice tight fit.