I know what Steve said about styli (Steve said lots of stuff ? - happy birthday eve, btw) but I think iPhone screens are now large enough - especially the Pro Max - where Pencil support begins to make sense. At that point, we would truly had a Field Notes-sized scenario - which I would LOVE.
For me, Pencil support on the Pro line is the feature I would like to see most. At this point, processing speed, camera, battery life - all of that is incredible. I'm less interested in little spec bumps than I am in additional capabilities. I'd love to be able to scribble out notes or sketches on my iPhone Pro. While maybe in the minority, I don't think I am alone.