I’m using jj for almost a year now and I definitely feel much happier whenever I need to rebase a branch or do an octopus merge. It really is liberating in an incremental way that creeps on you in day to day work. Don’t expect a revolution, though.
Small commits are the same small commits in jj as in git, you just split instead of add -p.
What does the magit interface for staging look like? I only used GUIs were you select the lines with the cursor or mouse and stage that. Is it like that or more sophisticated? Does it support editing hunks better, because that's a thing I only do on the commandline, because my Git GUI doesn't support that.
In magit, the diff is splitted into sections: Untracked, Unstaged and Stage. The sublevels are files then hunks. You can stage and unstage hunks, files and whole section by pressing s and u. Pressing k discards the node (section, file, or hunk.
You can also stage or unstage lines by selecting them first and press the relevan keys.
If you press ‘return’ on a hunk, it brings you directly the the line to edit.
jj wouldn't have any issues with supporting this workflow, if you could replace magit's git commands with some jj ones it'd probably just work. IOW the only thing that's missing is elbow grease.
actually, with jj's seamless rebases, it'd work exactly as you'd want it to (but maybe not how you'd expect if you're used to the git way) when aimed at a commit in the middle of a branch: pick lines which stay below, above or in the middle commit, which you can edit transparently.
The thing is that magit have a lot of commands that makes rebasing a breeze. Pressing c, then s, will allow you to select interactively (from the commits log) a commit to target when doing autosquash. That will create a new commit with the relevant message. Pressing c, the S (shift+s), will rebase immediately, squashing the current staging area into the selected commit.
Interactive rebasing is a breeze. Editing commits is very fast (reordering, dropping rewording, splitting,…). Same with dealing with merge conflicts (Emacs have various merge packages builtin).
The same speed Vim brings to editing, that’s nearly the same speed you get with magit for git.
Small commits are the same small commits in jj as in git, you just split instead of add -p.