Microblogs and threads are actually different activities. It's not currently possible to migrate them, and I'm unsure of the feasibility of doing so.
To delve into ActivityPub a bit, there are "actors" (like magazines and users) and "activities" (things the actors do). A posted thread is an activity of type "Page", but a posted microblog is an activity of type "Note". They then get stored in the database of whatever instance you are on, apparently as type "Link" as far as I can tell querying my SQL database. Still trying to figure out where microblogs go and how/whether they're different, how different things are stored...
But basically to promote or migrate a microblog to a thread, somehow the actual type of the posting would have to be changed.
To clarify: The threads get stored as type "Link". Actually there's a lot of interesting stuff in here - there's an "is_oc" column, tags column (weirdly empty even though according to the actual API you have an auto-generated tag of "kbinMeta"), and text search weights for various words (if I were to search the word "migrat" (sic), this post has a score of 22!)
I know I just keep replying to myself, but I never noticed there's an OC checkbox when posting threads - clearly that's what is captured in the "is_oc" column :^)
That's way more technical details than I expected! I really appreciate that as a developer!
I think in my mind moving a microblog to a thread was like copying the markdown text and pasting it into the thread container. And adding a link to the original micro blog post at the bottom of the markdown.
Maybe bonus if doing this also left a reply to the original post with a link to the thread so the original user is aware.
Ahh, that would make a lot more sense. Yeah, I'm sure something like that could be accomplished, similar to cross-posting.
There is definitely some cleanup work that needs to be done, in my opinion, to clarify the usage of microblogging vs threads. I feel like there's a lot of valuable discussion that gets lost in the microblogs. It's hard to have a single feed of both because microblogs don't have titles ("name" in the API), nor do they have any sort of summary that could be used as a title - making microblogs and threads just different enough from each other to be annoying.
Microblogs make much more sense on Twitter analogues such as Mastodon and Firefish where you follow people rather than topics, but I don't see a way to just follow a list of people via microblogs here - there is domain/sub/microblog (e.g. kbin.social/sub/microblog ) which follows your subscribed subs and people and maybe that's the best way to go here, but it still doesn't address the concern of "what is a microblog relative to a thread?"