What to do in case the answer has several comment threads, and merging them all into one doesn't make sense (or makes them too confusing)? Merge them by comment date, or thread creation date? Or just delete some of the threads completely (no value in keeping their comments)? Or is it just a very good sign not to convert the answer in the first place?

Andreas lost his angel wings‭ The 1st thought was to preserve threads, and add the answer converted to comment on top of each one. The answers which get converted into comments are usually short, so adding them to each thread shouldn’t clutter things too much. Maybe add an automatic explanation [apology for repeating] that this is an answer converted into a comment.

Andreas lost his angel wings‭ The 2nd thought was to flatten the thread structure, and combine all threads into one with the answer converted to comment on top. It would work for a majority of answer to comment conversions. Answers which get converted into comments rarely have multi-branched discussions where each branch is worth preserving. In most cases there at most one branch that discusses something technical that’s worth preserving, and maybe one more branch telling the author that he had posted a [worthwhile] comment as an answer.

I’m strongly opposed to duplicating comments, so if that’s the solution you’d suggest, I’d wanna see some examples. But the second one sounds better.

Andreas lost his angel wings‭ I haven’t got a preference for one approach over another. I haven’t got a real life example, because I haven’t seen an answer that needed converting into a comment, and itself had multiple comment threads. Maybe it’s a rare corner case.

Neither am I opposed to duplicating the comment (the converted answer) in these rare occasions. We are displaying one thread at a time. But it probably depends on the backend implementation too. I can make up an example, if you’re interested.