I've been thinking about what the real use case for TouchID, which on the surface is used primarily for security. Now that TouchID has been in use for a while, other uses have been created; however, I don't think that any of these uses actually touch on the true potential of TouchID.
As part of iOS8, one of the newest features is Family Sharing. Family Sharing allows a family to have separate accounts that are all linked together with the same billing information. This allows you to purchase apps for any individual member easily.
With Family Sharing solving the billing problem, the next thing that needs to be solved is how to allow a family to share a device, specifically a "family" device like an iPad, and do so in a simple, clean manner that Apple is known for.
From my perspective, TouchID fits that bill. With a fingerprint tied to an account, unlocking the device allows the apps for that user to be made available. With iCloud syncing, all of the configuration is made available at the same time. Now that the iPad Air 2 and iPad Mini 3 have TouchID as well, this seems all but a certainty.