Micro Led. It still likely will be in development for another 2/3 years at minimum, but I do forsee this being the next GEN display, I don’t think OLED will be a consideration for the iPad. The benefits for Micro-Led are significant with increased brightness, higher resolution and doesn’t draw as much power, which will result in longer battery life.
The tab S4 gets around 10 hours of battery life with a nice bright HDR AMOLED Display...no issues with battery life and thats on android (full day usage typically as well and I still go to sleep with remaining power around 40% and even better if just watching and streaming video/movies). There is no better display on a tablet device in my opinion than whats on the tab S4. I imagine the battery life with an oled display on iOS should be even better. You should not have to wait for microLED.....