- Node-based layer system, like Quartz Composer and Max/MSP. Right now, any complex nesting of layer styles has to be done via Smart Objects, which is a terrible hack that has you saving, seeing what the effect on the final image is, then going back and making more changes, repeat.
- It's 2012. There should not be destructive filters anymore. All filters should just be another node in this layout. If you'd like to apply them, you should be able to right click a node and merge everything that feeds into it. Brushes should also be usable as layers. Composite everything.
- Where's this layer system going to go? Obviously, it will go on screen, but how about an iPad app that pairs with Photoshop for displaying and altering it? They already have something sort of like this for tools.
- Photoshop badly needs usable variables of some sort. I'm tired of jumping around 5 different places because I decided I want to change a color.
- Going with the last one, documents should be able to contain multiple images, like Illustrator does. This would be a great addition for icon design, since you could (easily, without ugly hacks) have all of your sizes in the same document. Combine that with variables, and...
- Finally, stop the sucky non-native UI already. Stop replacing perfectly good Cocoa widgets with terrible Air ones.
Adding fancy new features is nice and stuff, but the fundamental UI of this application is getting really dated.