I think next year will be another refresh year as opposed to complete redesign year.
I think the magic will be in iOS 5 instead of the design of the product.
What I would hope for, most importantly is new home screen Widgets. Then an enhanced way for notifications to alert you. I am thinking a new interface that is more revolutionary than evolutionary as it has been since iOS came out on the original iPhone.
The whole OS, has really remained the same since its introduction, obviously things have been added since then. Had they not included wallpaper support in iOS4, it would look much more similar. The core apps, i.e. Safari, Music, Photo, App Store, etc., etc., are practically the same as they have been since they were introduced.