https://github.com/emersion/go-imap-sortthread now has support for threading so this could make some progress.
I'm not entirely sure how the design for threading inside the client would work, config option / command / something else?
A config option, you'll want to be able to set that to the default upon startup.
Commands aren't good for that
I could see some use in being able to flip between date-sorted and thread-sorted. For example you just want to see the latest messages and then use a command to see the previous messages in the thread. That's sort of like how gmail works.
I certainly would not object to just having a config option as a first pass.
... thanks sr.ht for stripping html that isn't even HTML for God's sake!
set category.option value