I would be OK with that, but even before you prioritize that feature, I’d be happier with a confirmation dialog on the Publish button. AFAIK, currently you only discover the slug by publishing and reverse engineering the header distillation algorithm.
In my case, I had already done a lot of work on the article, and when I hit Publish, I had expected a confirmation dialog, or perhaps a slug form field. It was only after publishing that I learned I couldn’t change the slug.
Another solution would be to implement an “Unpublish” button, wherein the article leaves the published state and forgets its slug. Then you edit the header and republish to get a fresh slug.
Yet another solution would be to allow a “copy” operation as distinct from “fork” which preserves the fork source target. I’d be happy with whatever’s easiest to implement.