Could also just support the delimiter argument like https://docs.djangoproject.com/en/1.8/ref/contrib/postgres/forms/ - although it's a little less flexible and requires the default error messages to change to be more generic.

I'm not entirely sold on this. django.contrib.postgres's SimpleArrayField is more customizable but this is mostly because the delimiter is not part of the database backend. In most cases I think it's probably better for the user to copy/paste the class and rewrite the validation logic because it's a bit tangled - realistically this pull request will only allow the customization of the delimiter and maybe the addition of simple things like .strip() on the input, which I don't think is really worth it.

Abandoning after re-reasoning the above.