Since everyone is giving their .02$ in predictions...
Here's mine.
ipod classic = drop; ipod touch will simply be called ipod with introduction of 128GB.
Nano will still be around. Its such a cool device still with mass appeal.
Shuffle could still be around. It is again a unique and novel product. It is something that is light, you can wear easily, and can withstand a lot of punishment. I dropped it many times and it survives easily. I know many people who in addition to one of the ipods, own a shuffle because they can take a shuffle to do outdoor activities or gym without worry that it could break. All other ipods are too fragile compare with the current shuffle. People will buy a shuffle the way it is, in addition to a nano, classic, or touch.
new ipod line; something to fill another gap or appeal to different people. a smart "watch" concept is interesting; especially one that would complement the nano, or ipod or iphone (as well as the shuffle).
I think there will be plenty of people who would still buy the ipod, along with a nano, along with the shuffle, and along with the new ipod. It does not need to replace any existing line.
Then again, it could replace the nano/shuffle... but I'm joining the fun with my 0.002$.
I think apple will extend their hardware line up of gadgets in such a way where we could buy one or more, so a 'watch' like ipod accessory could do this.
ipad
iphone
ipod (formerly ipod touch)
ipod nano (maybe a refresh with camera, more storage etc).
*rumored appletv/itv*
ipod 'watch'

P)
ipod shuffle
Pretty good line up for consumer gadgets to me.
... hmmm then again the classic may still be around until the ipod touch 128GB cost the same as the current classic. It is still expensive to buy a 64GB ipod touch today, the 160GB classic cost $250. BUT I would totally buy an ipod touch 128GB for $250 if it did came out Sept 1, 2010!