Described above (and gave examples of two mainstream libraries; with smaller one its much more serious). If there is a new package, its likely to be either totally not working on Python 3, or be undertested. So there is a delay, before I can use something with Python 3. (Nothing about the Python 3 itself, but about its ecosystem.)

At the same time, I hardy see any strong points, in which Python 3 is much better for data science. (Examples?)