I would also love this feature, honestly it’s strange that it’s still missing.
It doesn’t seem technically complicated, and it is extremely valuable. Without it, it is impossible to share links to my notes on the internet (knowing that most of them will break when I inevitably reorganize things).
Besides, by default the urls look pretty ugly (especially if you have notes with long names, spaces, capitalized words, and special characters in them), and custom links would fix that.
I think we should be able to add a slug field to the frontmatter, and use it to specify a permanent url for a page.
So that a link that looks like this:
https://publish.obsidian.md/andymatuschak/Andy+Matuschak/%C2%A7Enabling+environments%2C+games%2C+and+the+Primer
Could be made to look like this:
https://publish.obsidian.md/andymatuschak/enabling-environments