Development of major new features for Django tends to take place in branches — copies of the main codebase focused on a particular feature. Using branches makes it easier to experiment with such sweeping changes without possibly breaking master — the main line of development.
Branches may not be stable, but they offer a chance to test out bleeding-edge code before it hits the mainline. Give them a try, and remember to send feedback to the branch maintainers!
Since the move to Git, small features can also be developed in ad-hoc 'topic branches'. See https://docs.djangoproject.com/en/dev/internals/contributing/writing-code/working-with-git/ for more.
See DvcsMirrors for info about using other version control systems.