Most of the comments seem to assume TouchID as implemented today will remain the same in future. Here are a few scenarios that I imagine it may evolve to:
1) Unlock using multiple fingers;
2) Unlock using the same finger repeatedly, but with different pauses between taps, e.g. two short taps, followed by one long tap;
3) Unlock using finger gesture, for example press your thumb, then move clockwise 45 degree;
4) Unlock using a single finger, the iPhone sends a passcode to your iWatch with which you can use to enter.
Such uses of fingerprint would be much more secured, yet still relatively convenient. Losing your fingerprints wouldn't really be a big problem. You only need to change the sequence.
To further the idea, iOS may offer multiple accounts. Family members may have access to a "guest" section, whereas the phone owner has full access. Fingerprints can be used to unlock the appropriate accounts.
1) Unlock using multiple fingers; 2) Unlock using the same finger repeatedly, but with different pauses between taps, e.g. two short taps, followed by one long tap; 3) Unlock using finger gesture, for example press your thumb, then move clockwise 45 degree; 4) Unlock using a single finger, the iPhone sends a passcode to your iWatch with which you can use to enter.
Such uses of fingerprint would be much more secured, yet still relatively convenient. Losing your fingerprints wouldn't really be a big problem. You only need to change the sequence.
To further the idea, iOS may offer multiple accounts. Family members may have access to a "guest" section, whereas the phone owner has full access. Fingerprints can be used to unlock the appropriate accounts.