I've been driving a Tesla for 4.5 years with no rear wiper. I appreciate it isn't a near vertical hatchback, but I've not found it an issue. I also drove a mid-engined sports car for a while that had no rear window and got quite used to just using the 2 side mirrors.I think someone said you can press a button to have the reversing camera turned on whilst you are going forward at 70.01mph but then you can't wipe the camera from inside the car and as it is low down I'd be concerned road spray will mask its view at bit ( compared with walking speed when you are parking )
I used to be able to run the reverse camera while driving but that function got removed from a software update a couple of years ago. I have to say the view from the rear camera doesn't tend to get obscured by crap off the road, althhugh I expected it would.
Would I prefer to have a rear wiper on the Ioniq I've ordered? Probably. But I really do think you'll simply get used to it and that the reverse camera will suffice if you really can't cope without a clear view through the rear window. I think if the lack of rear wiper is a deal breaker for someone they don't want the car enough!