William,
So far, I see the main weakness of Write-In Only Voting to be coordinating voters written or typed preferences with the names of candidates. This is already being done most current election ballots, but usually with a trivial number of write-in votes.
By Minnesota state law, write-in candidates for local or city elections must be tallied. (In some cities, including Minneapolis, there are additional requirements for charter city offices.) For county, state and federal elections, the write-in votes are only counted if a candidate is registered as a write-in. Candidates must fill out paperwork at the Secretary of State’s Office to register.
Write-in ballots are counted at the city level. First, electronic ballot counters take digital images of the ballots and separate out which ones have candidates written in. Then, those digital ballots with write-in votes are sent to the city election judges to be counted. The entire process can take a couple of days.
Below, I discuss a possible method to address both of your Cases, but this is just a rough idea.
For both Cases (People or Machine):
Within voting booths, a digital ballot could be digitally filled-in by the voter on a computer (e.g. drop-down menu with a randomly arranged list of registered write-in candidates with clearly unique full names and no corresponding party), double-checked on a full digital ballot confirmation screen, and printed as a completed paper ballot as a triple-check. Then the paper ballot could be privately inserted into a counting machine and saved for a potential recount.
Determining requirements for registering as a write-in could be controversial. Voters could select the wrong candidate(s), but their fault after the opportunity to triple-check their ballot. A voter could be allowed to bring in (and leave with) a single example ballot with their favorite candidates secretly listed.
If Case 1 (People / Recount):
Misspelled and similarly spelled names would be corrected by using the digital drop-down menu. Identical names would be an issue for most voting systems with individual candidates, even with party identifiers.
The chances of misreading names would be less likely than hand-written write-ins and about the same as reading filled-in bubbles.
If Case 2 (Machine):
Counting machines could use an Optical Character Recognition (OCR) program to read clearly printed names on each paper ballot and automatically count them. If there is a problem with a paper ballot, then it would be hand-counted. For redundancy, the results of vote totals between digital ballots and counted paper ballots could be compared with any significant discrepancy triggering a recount.
Does this method address your concerns?
What would be fair requirements for registering as a write-in? Perhaps, petition signatures from 0.1% of the voting population.
How could it be improved?
Replying to your further comments: