forget 4-8”
The main reason I doubt we’ll see a 4-8” tablet (from Apple) is that it doesn’t fit in the tiny gap between powerful phones and net/note books. Smartphones do everything now, cost about as much as netbooks.
The touch UI is still wet behind the ears, and gesture-based interaction will be tough for many users to swallow, so while an Apple tablet would be really cool the market probably isn’t ready.