There were some dreams that the Python 2 to Python 3 migration would happen for Ubuntu 14.04 LTS so that Python 3 would be the default, now two years later, it looks like it might finally happen for the Xenial Xerus. A session was held today during the Ubuntu Online Summit for migrating over to Python 3 by default and to no longer ship Python 2 as part of the default package-set.
As can be seen from Launchpad, a lot of work is still needed before Python 3 only as the defaukt will happen. The work is a mix of dropping unsupported Python 2 packages to porting other packages to Python 3 compatibility.
More details on the planned Python-3-only migration can be found via today's session notes.