It's been looked at (my advisor in grad school was working on it) and it keeps running up against the problem of scaling -- 100 million transactions (800 million if you want to scale up to India) on a single day is going to be hard from a realization standpoint, even if it's theoretically doable.

There's also the interesting psychological side to it: while a blockchain system is in a theoretical sense more transparent than anything else, from a popular standpoint it's incredibly opaque compared to a county registrar counting two different stacks of paper ballots.

Yes, Dash (DashPay) has been up and voting on stuff for a couple years. Because I own 1,000 of the things I get to vote on stuff like sending devs to conferences and different ad campaigns to run, then the winning bids get paid out of the block reward. If we vote no the Dash just gets destroyed and inflation is slightly reduced.

I like the idea. There's some funding waiting for that innovation

There are several voting systems built on top of Ethereum.

Especially if done using a ZKP like ZCash supposedly does. That would be great.