I think you mean PKI. Two factor authentication is not secure, nor convenient. You are forced to keep your phone with you and type crap from the phone into the computer. Meanwhile someone can port your phone number and pretend to be you.
The advantage to the voter would be the ability to retain a file showing their ballot choices, and the unique identifier of their ballot.
Illegal and not desirable. People could more easily sell their votes.
Each completed ballot in the database would have metadata showing its unique number/ID, the precinct associated with the voter account, a timestamp showing when it was uploaded,
Not good. Experts could figure out individual voter's votes from that info.
Other commercial and government databases would be periodically cross-checked against the database of online voter accounts, to identify and notify voters who moved without updating their accounts, became felons, or died. (Yes you should be notified if the system thinks you died, in case you didn’t) Voter accounts would expire after ten years unless the voter renews by making another in-person appearance.
Ten years is way too long. But the suggestions there are good. In fact that is what we need to do and is missing from the OP's article. Also third parties need to have the ability to cross check, from both parties. The data must not include people's votes, but all other registration info needs to be given to third parties who can cross check across jurisdictions, other databases, etc.
No, I mean 2FA. It could be done with Google Authenticator, being emailed a link to click, receiving a PIN via text message, or answering a security question.
People could more easily sell their votes.
That already happens, and the price is usually a couple packs of cigs or beer money. The street people who sell their votes are highly unlikely to go through the procedures to become online voters. They will be paper voters, if anything.
Experts could figure out individual voter's votes from that info.
How? The file connecting the ballet metadata to the voter would not be available to "experts" unless they show cause and obtain a court order for any inquiry.