Git compatibility pretty much rules out the radically different approaches that might actually be better enough to outcompete it. Like:

- Patch-based VCS (darcs, pijul)

- CRDT (live collaboration)

- Image-based systems (Smalltalk)

- Features that require the server to do stuff that Git protocol won’t do, like push notifications

In other words, I can’t imagine leaving Git unless it’s as big of an upgrade as Git was to SVN. And you can’t do that while being wire compatible.