For example if I add an additional usage to a global variable to a file, while someone else renames it in other files, git happily merges with no conflict.
Tighter language integration can help with that.
For example, I have seen cases with diffing where based on whatever algorithm, a very small logical change, (like moving a function up or down in the file along with a minor edit), creates a very confusing side by side diff based on whatever similar lines it think match up.
I would very much like for this not to be true, but there doesn’t seem to be a good solution.
With syntax trees in particular, it’s also frequently difficult to find even a single good option for what you would reasonably want a diff to be: last I checked rich-text diffs usable over arbitrary HTML (even sans CSS) still sucked in half the cases you’d want. Line- and word-based diffs over the source also suck, naturally, but at least they do so uniformly. It’s not an accident Stack Overflow will usually try to show you a rich-text diff when editing but will occasionally fall back to word-diffing the Markdown.
And a version control system needs to interoperate above all. Unlike, say, an IDE, and you do see attempts at semantic and even structured editing in IDEs.
/me continues to fantasize about interbreeding Paredit and Pijul one day