Python 3.3 has implicit namespace packages (PEP420) and in Python 2.7 packages can be marked as namespace packages through adding two lines into __init__py. See How do I create a namespace package in python.
Given the features the packages enable, it looks like that new packages should be created as namespace packages by default.
Normal python packages should only be used in exceptional cases where the need for a "closed" package is obvious.
What would be drawback of this approach ?