This. I feel jj is some years too late.
It tries to solve a human problem in an LLM era.
LLMs are destined to overcome humans in code merging and change versioning (already did for me).
There's little point to introducing yet another layer of indirection when LLMs just cut to the chase.
Good git hygiene is also less important post-LLMs, as the LLM can make sense of even a messy history.
A lot of humans don't currently trust agents to touch VCS today. I also find that my agent tends to be much better about dealing with jj than it is with git.