One thing that I think could work and obviously make a few parties upset would be a "maximum stake". Once your account reaches a determined amount of vests, that is all you can vote. Sure, you can hold more steempower than that but they don't count in the stakeweighted voting.
Interesting thought, but what would people stop from having multiple accounts until this threshold instead of 1?
Checkmate! Damn!
Maybe make the max stake dependent on the reputation or the account age.