I'm looking into purchasing an ASUS Zenbook Prime UX31A-DH51 and shifting it's win8 preinstalled OS into a clean linux install.
Besides the known issues of linux support of this endeavor, how would it be possible to keep the whole win8 installation cloned on some external storage, just in case something goes wrong or I decide to give\sell the device to a non linux user?
You have two options:
1. Take an image of the drive and store it somewhere safe. There's a ton of free utilities that can do this, including one in Windows 8 itself.
2. Wipe it completely and reinstall it later. The serial number that comes with the device is an OEM licence, it' belongs with the device rather than the user. Windows 8 can be reinstalled as many times as you wish on that same device. Asus may even have the key embedded in the motherboard firmware (SLIC table) which bypasses the need for activation completely.