I believe the curved design and larger screen will definitely make it into this update, and I feel this way because of the lengthy delay and the iPhone 4's beautiful but flawed antenna design.
Uniformity is what Apple has been going for. Merging iOS and Mac OSX is the first hint towards this.
I believe the next generation iPhone design will follow suit to the iPad 2 and Macbook Air designs.
We will see a revamped iPhone 5, iPod touch and thinner Macbook Pro come later this year, with all designs being uniform.
Both the iPhone 5 and next gen iPod touch will be all aluminum, curved back, larger screen.....basically smaller versions of the iPad 2 design.
The Macbook Pro will follow suit with the Macbook Air, with an all aluminum look, thinner design, retina displays and perhaps no optical drive and standard SSD.
Then finally come spring time next year we will see the iMac line follow suit with retina display, no optical drive, standard SSD.
Perhaps about the same time an iPad 3 with a retina display as well?
Uniformity, simplicity, I believe this is the future of Apple products.