Whether there will be more customizations in iOS 8, I don't know. Like Highrisedrifter, I'd like a few more themes, but I'm really hoping they'd revamp the Mail app to be in-line with that of a desktop, especially in regard to mass selection, and the ability to attach any kind of file from within the Mail app itself.
A dark theme, ability to attach multiple files onto an email that aren't the same file type directly from the mail app. Color choice for control center and the notification center instead of using the color of the background.
I'd like to see more control over animations. The way it is now is all or none. Some like the stock Weather app animations but not the Parallax Effect. Separate toggles for the different animations would be great.