Apple may have found a niche between the smartphone and laptop, but the general trend is towards convergence. What is the logical endpoint of this? I think the smartphone will become the only device and all other devices will become smartphone peripherals.
Instead of a tablet PC, you have a 10" touchscreen that your smartphone slots into the back of. The screen provides some extra RAM and processing power if necessary.
Instead of a laptop, your touchscreen mentioned above has a clip-on laptop keyboard and touchpad. Again the body of the keyboard can provide some extra RAM and processing power if necessary.
Instead of a desktop, your smartphone connects wirelessly to your 24" screen, which is connected to a mouse and keyboard (and other peripherals). Again the screen can provide some extra RAM and processing power if necessary. Obviously if a larger screen in not necessary, then the 10" touchscreen mentioned above can dock onto a monitor stand (with connections to the mouse and keyboard) and then connect wirelessly to the smartphone.
Instead of a dedicated music player, you have speakers that wirelessly play music from the smartphone. The smartphone only contains enough of a music collection to tide you over being out of connectivity, but the smartphone can stream music directly from the internet.
Instead of a DVD player your TV (just another large touchscreen, or projector) plays video wirelessly from the smartphone. The smartphone only contains enough of a video collection to tide you over being out of connectivity, but the smartphone can stream video directly from the internet.
Your smartphone also wirelessly communicates with your fridge, washing machine, cooker, etc over wifi. When you are out-and-about, the fridge can still talk to your smartphone via the wifi box and internet connection (and 3G connection to the phone).
Instead of a landline phone you have, a smartphone which should be able to make VOIP calls.
What needs to happen to get us there
More processing power in smartphones
More RAM in smartphones
More HD capacity in smartphones (500GB of flash memory should do it)
Faster data rates for wifi
Better online music/video systems (to be discussed in a later post)
More cloud storage of data