OLED instead of LCD is one improvement that the Quest 3 could have. Quest 2 is suppose to have the best type of lenses, but I guess they can improve that too. And finally, they can improve the FOV (but for porn, you are looking at one direction usually). Adding codec support for AV1 would be good too, as it is suppose to be more efficient than H.265.
That being said, I would still be happy with the Oculus Quest 2 for the next 5 years. It's price so well. Other headsets may come out, but could be priced much higher. 6k, 7K and 8K already look amazing. Before the quest 2, I don't think there were any standalone VR devices that supported 8K video. So 8K is new, and is likely not going to be higher for more than 5 years. AMD GPU/APUs haven't even supported hardware 8K. Their newest APUs, ryzen 6000, do, but they are just hitting the shops, slowly. NVIDIA GPUs had 8K since 1000 series.
https://www.sexlikereal.com/scenes/vacation-19148 this video 8K video, the 40GB version, looks amazing on the quest 2. It may have been the first 8K video I saw.