Definitely need to be able to see the brush size when retouching. The only way at the moment to see what size brush you have is to scrub the brush size to get the cursor to show. A lot of guesswork And poor results. Affinity photo does not offer this either. I think if adobe photoshop mobile provided this, it could bring in more customers on the ipad and convert Affinty users.
Curves, to give us a little more adjustment control and to allow dodge and burn!
Mixer brush, because it fits in with the convienent "mobile" editing workflow.
Filters or preset actions like affinity photo provides. We need to be able to apply filters for frequency separation actions like guassian blur and high/low pass.