Wouldn't most current block-chains tie a rather fine (say 5-minute, accounting for drift) timestamp to each vote? So in small voting districts, if you had a way to know approximately when people voted, you could go a long way towards de-anonymizing votes (say, you managed to track someone's device, that they used for voting, or track their location, if using dedicated voting machines)?

I don't know if it would be inherit to making a secure voting system on a block-chain that you had such (unnecessary for voting) fine-grained timestamps, but just a thought.