I really don’t think it needs oled or thinner. Oled risks burn in (I say as I have an oled desktop monitor without burn in, but I worry about it) — though perhaps Apple can figure that out (micro led would be great though). As for thinner, it’s pretty dang thin already. I’d rather more battery in the 14” and be a little thicker, honestly.
Apple seems to have it figured out, my last two iPhones have had OLED screens and I never saw any burn-in despite having them on a lot and fairly bright.
I don’t think burn-in is much of an issue on modern displays. When was the last time you’ve seen a phone or monitor with burn-in?
I think it’s still a very real issue, even if it’s less of one than it used to be. I haven’t seen any phones or monitors with burn-in in person, but the only OLED monitor I see on a regular basis is my own, and phone screens pose less risk of burn-in in general, since they’re not getting used continuously for 8+ hours a day, nearly every day.
Apparently burn in is much less of an issue on the dual stack style the iPad has