Transparency of votes doesn't have to map to identity of voters. The blockchain is transparent, what you put inside is left to the implementer to choose.
And come on, it's a highly experimental technology whise use cases impact the most controversial aspects of our society : money, vote, accountability, transparency, power to the masse.
Of course it's going to take time and fail in many spectacular ways.
Full public transparency isn't that great a property of a voting system.
And it's hard to call it a "legitimate use case" before it's successful.