Bzzt. Wrong.

The obstacles are:

1) Battery lifetime/power source, as you said.
2) pocketable/phone devices with enough CPU power and CPU compatibility with desktop apps
3) pocketable/phone devices with KVM capability

If your phone had enough CPU power to run the same apps as your desktop, and still keep enough battery life (through battery capacity and/or CPU efficiency), and you could plug it into your KVM switch, and/or into a docking shells/companion-devices that had the shape options of (slate-tablet, netbook, laptop, full-desktop), then you don't need "shape shifting" technology. You pick the shells/companion-devices that suit your needs, and go from there. 1 CPU/storage device for all use cases.

And, there are actually 2 other limits that will keep us from fully replacing desktops and laptops with this "one device":

4) storage density -- you'll always be able to put more and faster storage into larger devices. The best you can count on here is: having storage density improve enough that you don't _care_ about being able to store more at home.

To some extent, 2-4 can be off-set, somewhat, by moving applications and storage into the cloud. Which brings us to the 5th hurdle:

5) network ubiquity -- you can't displace the other factors with cloud storage, cloud computing, remote access to your home storage, etc., without an ever-present, affordable, broadband network. Don't count on that happening any time soon.