Django absolutely would have been ported: it was ported without six by Vinay Sajip (building on an earlier work of Martin von Löwis). In fact a limited shim layer was initially committed based on Vinay’s efforts: https://github.com/django/django/commit/5e6ded2e58597fa324c5...
The team ultimately decided to use and re-export six for the convenience of the ecosystem, not out of any sort of necessity.