So I am a die-hard OPD fan. IMO, paddles are gimmicks. I can see how it could help someone transition from an ICE but I am a rip the band aid off kind of person.
I have never driven a vehicle that had seamless blending between regen and friction brakes. In the Tesla and Volvo worlds, the brake pedal only actuates the friction brakes; the accelerator only actuates the motors. It's also simpler for the manufacturer - keep the systems separate.
In that downhill scenario I want to know if and when I am using friction brakes so I don't overheat them.
In the freeway scenario, cruise control will handle the times when you should be coasting. One thing about EVs is that there isn't a huge penalty for holding a set speed up and down hills. In an ICE, if you are going up a hill and slow down enough that the car has to downshift, your mileage will drop a fair amount as the engine must rev a lot higher. EVs don't suffer from that. Plus on the downhill it will automatically regen to keep the speed so you don't have this constant yo-yoing of slowing down up a hill, then speeding up down the hill, lather, rinse, repeat. With an EV, you just drive the vehicle.
For me it's just completely seamless and intuitive. I almost never use my actual brake pedal. Just the one foot on the one pedal - push for more, ease off for less. You don't even think about it - the car just instantly responds to your whims. If you are the kind of person that treats the accelerator like an on/off switch then yes, you are going to make people nauseous. Just don't drive like that - it's the wrong way to drive.
This is why I really hope that they put thought into both viewpoints. I know lots of people love one pedal driving, and I of course want those users to have a good setup/hope that its implemented well there. I just also don't want that to be the only well defined option.
I have a friend I drove to work with once, who did treat the pedal like a lightswitch (F150 Lightning). It was literally every 2-3 seconds, a herky jerky sensation forwards or backwards. And that was nauseating (hence why I've only driven with him once).
I like to think I'm much smoother than that. Like you said, thats the wrong way to drive in general, in any vehicle. But even then, I notice that in the most aggressive regen mode (level 4, which is Hyundais 1 pedal mode), that it takes a lot more effort to stay smooth with. So far, no complaints from passengers either way, but as a driver, I'm finding its easier/less fatiguing to control in the part throttle application scenarios, with less regen baked in.
I agree though. I do wish it was easier to tell when friction brakes were engaging. Even something like a dashboard light, or a visible threshold being reached would be good to know.
On our Ioniq 9, when you use the brake pedal you can see the "power/regen" dial (the thing that exists in the dash where a Tachometer would normally go), and you can see it sweeping the "dial" farther and farther into the "charge" region of the meter. Even adding something like a "red line" that showed where the brakes were engaging would be helpful.
I personally, I'm worried mostly about one thing with one pedal driving. Once you get out of the muscle memory of using the brake pedal, and covering the brake pedal, I can see how in a panic braking situation the instinct may just be to "lift off" the accelerator, and not actually mash the brake pedal. Not sure how it is in other EV's, but while the max regen setting (the one pedal mode) for my Ioniq 9 is fairly strong, its nowhere near panic braking levels of stopping distance.
I know that there are a lot of collision avoidance systems now, which may do some of that for us. But I also know I've seen enough videos where those systems are tested, and failed, that I know I'd want to make sure I am prepared to smash the brakes asap if a deer/cyclist/kid/whatever needs to be avoided.
Perhaps its because I know my personal "instinct" and muscle memory is pretty baked, and just don't want to mess with it (and I'm not saying you/others are not, I'm just speaking for myself here). Especially with not all of the vehicles being EV's (one EV, one PHEV, one 30 yr old gas vehicle).
In college, I'd been driving manual transmission cars for a while, and my parents came to visit, and I drove their minivan (with an automatic transmission) to go do something. I got into a panic braking situation. Someone pulled out into traffic aggressively/unsafely, and my panic response... was to smash the dead pedal with my left foot, and "downshift" with the water bottle in the cupholder in the middle (again, I was used to a manual. I freaking STOMPED on that dead pedal, and my hand apparently grabbed whatever was in the general area where a stick would be). I got a giggle out of that one.