The default user model is fine, but I *always* start a project by extending it, for future-proofing. If you need to add to it, this is *so* much better than having to add a one-to-one, and at *some* point down the line you find you do want to add something. The problem is that doing it later when you need it is a pain, because of poor support by the migrations framework.

It's like 4 lines of code that saves you so much grief later on:

    from django.contrib.auth.models import AbstractUser
    class User(AbstractUser):
        pass

    AUTH_USER_MODEL = "myapp.User"

If you never need it, those 3 lines are not hurting you. In terms of a default, I think it probably would be nicer if Django pushed you to do this up front.