Reflow in the sense of wrapping blocks of text? That exists, I think under :reflow, although I always forget the name when I'm looking for it.

[keys.select."space"] q = ":reflow"

has worked well for me, even if the reflow behaviour itself is sometimes frustrating

this is the kind of thing kakoune (helix's primary inspiration) excels at --- i can hook `fmt` to a non-whitespace character insertion and have auto-reflow as i type. of course, this requires the user implementing the script to get it right, but then you can pr it into kakoune's "stdlib" which gets loaded by default, so any user can use it. (though helix is getting a plugin system eventually, which hopefully alleviates the pain of slow merges.)