2 things:In my experience, once you see OLED, you don't go back. My literal first OLED device was whatever iPhone had it first. Even with the small screen size, it was a revelation for me. Next, the TV was upgraded. Then my desktop monitor. Of course, as soon as relatives visited and saw the OLED in action, several are planning their next purchase to be an OLED. It's just that good. I regret not getting OLD on my bedroom backup TV, but it's still nicer and rather new so I can't justify the replacement.
iPads? No thanks. My kids each have iPads (Air). I would never in a million years trust them with an OLED screen. You really don't need to baby them, but they would be abused by kids who don't think to press the lock button and regularly leave static games running on accident. The only people I know with iPads have them for their kids.
I would not expect OLED iPads to be great sellers. I could be wrong, just my opinion.
1) I still keep my 2011 55" Panasonic Plasma TV around in my bedroom because I watch a lot in darker environments and absolutely love the inky blacks. I hardly watch any tv otherwise these days, so the main living room TV is a Samsung Frame which is really more for aesthetics than real watching.
2) When it comes to iPads, I think the idea would be to only have the iPad Pros be OLED, with the Air and standard versions LCD. I have 2 young kids and they both have iPads (1 has the 10.5" iPad Pro and 1 has the 9th gen iPad). They thoroughly abuse it. I also use my 2018 11" iPad Pro as one of my primary consumption devices, especially in bed / at home. I think there would be a market for both.