It seems like they could add a few less-predictable factors to improve the security of thumbprints without completely ruining their convenience.

For instance:

— Maybe you must use two or more particular fingerprints in sequence, selected by you in advance. This would require a “sleep attack” to at least try different combinations of your fingers (without knowing which to use first or how many fingers are required).

— Maybe you have to hold down your thumb in a pattern that you set in advance (e.g. at least 2 seconds on, followed by one second off and one second on).

— Maybe a 3-by-3 grid appears and you have to tap one of the squares that were set in advance by you before using your fingerprint. This is faster than having to enter a whole pass-code but slightly stronger than just tapping a finger.

Of course, each of these trades off time (convenience) for slightly better security.