I looked this up and for anyone wondering, it's called "diff/merge drivers", but there are only a handful of them out there. Some highlights from a few minutes of searching:

- MS Office: https://github.com/lcnittl/DMFO - SQLite: https://github.com/cannadayr/git-sqlite - Jupyter notebooks: https://nbdime.readthedocs.io/en/latest/vcs.html#git-integra...

One big caveat of this is that since git doesn't really store just a stack of diffs, despite the fact it presents itself as such to the user, a custom merge driver will not make your .git grow any less than it would normally.