The odds of having a Blockchain-based election are zero to none. Governments have other important things to work on, especially finance. They could launch a private blockchain network of their own in order to issue digital currencies to their citizens. It's better for them to use Blockchain tech for finance and proof of ownership, than mainstream elections. We all know that it's difficult to manipulate the Blockchain because of its transparent design. The old-fashioned way of voting will always be the choice of worldwide governments as it's much easier to rig election results. This is most suitable for organizations or companies than governments themselves. The power of smart contracts with the Ethereum blockchain opens up a world of possibilities that were never imagined before. Elections performed on a public blockchain like Ethereum are much more secure and tamper-resistant than those performed on a private ledger.
But who knows? Maybe governments find out a way to manipulate elections while bringing the convenience of Blockchain technology to voters. If everything goes full Blockchain, then I don't see a reason why this shouldn't happen in the first place. As adoption for Blockchain technology grows, governments will be able to provide services on it. But we cannot deny, that Blockchain works best when it's used for finance than anything else. Just my opinion