A note from Guido, from about 2 years ago:

https://mail.python.org/pipermail/python-dev/2012-July/121127.html

"""
TBH, I think that adding nanosecond precision to the datetime type is
not unthinkable. You'll have to come up with some clever backward
compatibility in the API though, and that will probably be a bit ugly
(you'd have a microsecond parameter with a range of 0-1000000 and a
nanosecond parameter with a range of 0-1000). Also the space it takes
in memory would probably increase (there's no room for an extra 10
bits in the carefully arranged 8-byte internal representation).
"""

Add pickle, etc.