There are multiple tells that this move, just like the removal of radar, is supply-chain and cost-driven and not actually driven by engineering. If this were a planned move, the software would already be ready to replace it. It is not. Cars without radar still aren't at parity with the car that have it, although they "fixed" this a few weeks back by simply turning off the radar on the older cars. The parking sensors…
It would be possible to use cameras instead of ultrasound, but that would require mounting a lot more cameras in the dead zones as you said. One of the coolest things I've seen was on a BYD, which has cameras mounted pointing downwards all around. It then creates a fake birdseye view when you are parking, or close to an obstacle. It looked really convincing, as if there was a drone above the car.
I mean damn that looks legit. I'd like to see how it performs at night when you're trying to park in some unlit parking lot, but otherwise that's a pretty amazing projection right there. The dream of driving in 3rd person view is finally here.