The author doesn't know how to use git or how git works.
If he knew how to use it, he'd be annoyed at some edge cases.
If he knew how it works, he'd know the storage subsystem is flexible enough to implement any kind of new VCS on top of it. The storage format doesn't need to change to improve/replace the user facing part
Joe Armstrong had a beautiful LEGO vs Meccano metaphor. Both things are cool and somewhat similar in their basic idea, but you cannot do with LEGO what you can do with Meccano and vice-versa. Also, you can not mix them.
But you could create some parts that are enabling you to combine them easily. Which is what you could do with software. Write an adapter of sorts.
Sure you can. Hot glue, E6000, duct tape. This is to say, git's pack format has its shortcomings.