Earlier quoted context omitted.
> Except for HN, Twitter & Reddit, are there any services that don't use email for login? I guess sites that use the username as a form of identity within a site. Email address usernames are just identifiers and contact information, without really being linked to an identity. I would think if auth was being written from scratch it'd probably default to email based usernames. That ship has sailed though.
But it shouldn't have sailed. Frameworks need to keep up with the times. That should be a benefit of frameworks. Should be possible while preserving backwards compatibility.
Which meant that Django's database models couldn't migrate.
Even now, there is no real way to start with Django's own User model and switch your project over to a custom one later (because you'd have many database tables with foreign keys to the Django one). The current recommendation is to start new projects with a custom User model always.