How plausible is a new voting algorithm that reduces rewards if you vote the same person more than twice in 24 hours?
Not plausible at all, unfortunately. This is an example of a hard fork solution, and it's something we should try to avoid. Fixes like this would only siphon even more inflation to the whales because they are highly motivated to sidestep such regulation.
Meanwhile, average users who have no idea what's going on get penalized and would then be distributing less inflation than before. Who now controls those extra rewards that got taken away from users that don't know any better? The whales who know exactly how the system works. They'll just make more accounts to get around your regulation and your idea will ironically backfire.
The only way for proof of brain to happen is with consensus. I know this will be easier to achieve if we target one abuser at a time and bring them into the fold. The movement will grow when we show that we are scalable and none of the abusers can get away with their bad behavior.
Greed is contagious. One bad actor spawns 100 more. If one person cheats (at anything) this makes other people feel left behind and cheated, so they justify the behavior. It's time to reverse the polarity of this toxic dynamic. We have to make the behavior unprofitable for users one at a time and compel them to join us to stop the rest.