Scenario: A particular community/religious institution/school, etc., lets their members know (not in writing) that they will be required to have their vote witnessed by two other members, on pain of expulsion.
This is not far-fetched, even in some places in America, and certainly in other countries. Even if we can be 100% certain that the vote is secure and not tampered with online. I don't see any realistic technological solution for this. Giving the option of in-person or online voting won't solve it - those wishing to coerce will simply require members to pick the online option.
Yes, this is already possible with mail-in voting (and there are reports of it happening.) But if online voting becomes mainstream it will become a much bigger problem.
Disappointed that the article didn't mention this at all. Reminds me of https://xkcd.com/538/