"Python 3.0 final was released on December 3rd, 2008."
- Python 3.0 Release notes
"The End Of Life date (EOL, sunset date) for Python 2.7 has been moved [...] to 2020."
- PEP 373: Python 2.7 Release Schedule
Migrating to Python 3 is not a big bang, it's a sequence of steps, like the rungs of a ladder that spans from 2008 to 2020.
In 2015, many people still start new projects in Python 2. Many of us are shackled to Python 2 for work. Some of us don't even have a migration plan. Many people at this conference, if asked to run "Python", will launch Python 2.
Daniel will encourage you to grasp the ladder, put your feet firmly on it, and take the next step in climbing to Python 3.