Security is always a balance between false positives and false negatives. You have to err on the side of locking out an authorized user for obvious reasons.
With typing cadence people will soon learn to sit down and type normally, especially after you tell them that and they still try it one-handed, standing up, in the dark, drinking coffee, with the cat trying to get their attention.
Password programs are becoming more draconian, they already require a mix of upper case, lower case, and numerals. It won't be long before they have to be of the form A9#9#A. Then of course we'll all forget them, especially since they force us to change them every 90 days.
Passwords just can't provide the security we need without overwhelming the security staff with requests for new passwords, a situation which creates quite a risk exposure of its own.
I predict that biometrics will replace them. Voice prints have the problem you already identified. Your retinas can be removed and stolen if this is a James Bond scenario. Personally I think typing cadence is probably the best way to go.