Pijul (https://pijul.org/) is based on a categorical theory of patches (https://arxiv.org/abs/1311.3903). It is similar to Darcs but written in Rust. They claim that Pijul has solved the exponential merge problem. The docs, FAQ, and blogs, in particular the last one, are interesting readings.
Anyway, once you get rid of the actual complexity in git, it's an easy step to work on the added complexity to the UI.