There would be absolutely no reason to root the Fire. It would become totally useless. The device supports 8gb of on board memory. About 2gb will be taken by the Android operating system, and another 1gb set aside for apps. Without Amazons cloud backing it, you'd have only 5gb of usable memory at best. Plus rooting it would be a total pain because the only way to root would be by using the foreign method of adb through the usb cord. And you need dedicated developers.
If your sole purpose for this tablet is to root it, why not just get a Nook Color? It would be easier, the rooted OS is a year into development, and can be found at a cheaper price