* Regarding "splitting commits in an interactive rebase is hard" - I actually use `git reset` (to unmake a commit) followed by several instances of `git add -i` (to add individual changes into a commit) + `git commit` (to actually make the commits). If the commits to be split are in a middle of something, it's possible to do all of this inside a `git rebase -i`...

...which is exactly what is suggested in the section linked in the article, https://github.com/kimgr/git-rewrite-guide#split-a-commit.

* Regarding "weird interactions with merge commits" - `git rebase --rebase-merges` tends to help most of the time, since, during a rebase, merge commits are skipped by default (even if they contain changes).