Please write the spec for next generation version control.
I feel like Git is great but we could have one which is easier to use and has built in concepts like Pull Prequest or deployed state.
This is a short-sighted view in my opinion. Similar views often lead to reimplementing old bugs, rediscovering hidden requirements, and ultimately re-implementing most of the things that made the old system complicated.
We've seen this in npm. Npm was supposed to be simpler than maven - then it slowly rediscovered the reasons we need package signing, support for circular dependencies, and all the other messy things that go into package management.
While I don't have numbers, it seems like a huge percentage of the "this problem should be simple, let's build a new app" projects either fail or recreate the same gnarly problems that led the existing projects to be complicated.
There's a plenty of better*-designed systems, problem is no one (except a few opinionated geeks) cares [enough] so they're unlikely to ever beat Git unless a miracle happens (aka a major industry leader will make something trendy by promoting it).
For example, Darcs (older) and Pijul (newer) are based on patch theory, so Git's rebase issues are moot there.