I do believe this. But that doesn't mean I can't be convinced otherwise by a good argument. The point of this post is to see if anyone has a great counterargument to change my mind.
For users it's a set of scales that hangs in balance. On one side is the disruptiveness of the change to them, and on the other is the promise of what they will gain once on the other side.
If there's a problem with the current thinking it's that it proposes to trigger a big expensive breakage that we'll be paying for for 10 years, but there hasn't been any serious discussion of what else is broken about git that needs to be fixed to git to continue to be relevant for the next 10 years.
Most discussions are pre-constrained by the idea that ecosystem wide breakages are impossible.
In theory it's good for me if the git ecosystem splits compatibility in half with no obvious benefit. That just makes it easier for me to waltz in with a third backwards-incompatible migration path, one which actually offers eye-popping kinds of benefits in return for the cost of the breakage. That's why I'm competing with you in the race to replace Github. It's just that I'm also racing to replace git, so I assume you'll be in some amount of trouble if I should succeed.