crowning thelonecrouton vertoe kryptofoo TsuyokuNaritai
The problem here is to find equilibrium between a low probability and high impact event (double spend), and a higher probability and lower impact event (fall back to block confirmation system). It is true that a super majority or a redundant list would greatly reduce the probability of the fall back, but it would increase the probability of a double spend by forging the lock. In the super majority system because you need a lower percentage of the selected masternodes. In the redundant list system because the attacker could DOS selected masternodes that are not his so he has a new chance to get one selected.
I'm out of town in a weeding for the weekend, but I'll think about it to run a few numbers next week.