Something I'd have done differently with 1999.io was skip trying to make it multi-user. Adds complexity and my feeling is that very few people were looking for that. Perhaps Dave was.
This shows itself in URLs. Note that I'm serving this site at 1999.baty.net but the links generated use the full urls, including the user path /users/jackbaty/2019/09/06/. That should instead be /2019/09/06/
Interestingly, this how-to indicates that there's a way to not use the long URLs. Unfortunately, when I configure it, the top menu of my site disappears and I get 404s at all the original (long) URLs.
Testing a publishing callback. (didn't work :()