Phones and PC browsers are good enough for electronic banking. A vote is worth less than the contents of your bank accounts.
Blockchain can resolve many of the problems of centralised servers being compromised and allow for anonymous auditing of votes after an election.
The biggest issue I see is that it makes coercion possible when someone can be forced to vote in front of you as opposed to in a booth where you can’t see what they are doing – but so does postal voting. There are some schemes that address this by allowing people to vote more than once with only the last vote counting.
Probably the biggest opportunity from electronic voting is that it would remove the constraints of paper based systems and allow more flexibility in the whole process of selecting representatives to make people’s vote actually count. For example, you could have a two stage system where first MPs were elected but then everybody got to decide which of the MPs in parliament should represent them (rather than being stuck with the one from their constituency). When MPs vote in parliament their vote could have different weightings according to the number of people who had selected them. If, in the middle of a parliamentary session, your MP really p*sses you off you could switch to another one.