Django 1.8 will come with new advanced field types including ArrayField these rely on PostgreSQL and are implemented at a DB level.
PostgreSQL's array field implements an append method.
However I can't find any documentation on appending an item to an
# on model:
tags = ArrayField(models.CharField(max_length=200))
# somewhere else:
p = Post.objects.create(tags=[str(i) for i in range(10000)])
I think the features you are looking for are currently not implemented (and may not be planned). Many of the Postgres contrib features originated based on this kickstarter project.
An important note in regards to the Array Functions mentioned, they are Functions and arguably outside the scope of a typical ORM.
I hope this information is useful and you find a nice solution to this issue.