I have some (additional) concerns here:
That’s enough information to make some votes unique. So if your vote becomes known elsewhere (e.g. because you publishes your preferences, or you only support your own proposal, or you voted on the forum and that gets compromised), then you’ve effectively broadcast how much ZEC you hold (or at least a lower bound on that).
Also, there are ZEC lending markets, meaning this balance-snapshot vote can be grossly manipulated very cheaply.